Adjustable Pulse Characteristics for Ground Detection in Lidar Systems

ABSTRACT

A method in a lidar system for scanning a field of regard of the lidar system is provided. The method includes identifying, within the field of regard, a ground portion that overlaps a region of ground located ahead of the lidar system; causing a light source to emit pulses of light; scanning at least a portion of the emitted pulses of light along a scan pattern contained within the field of regard, including adjusting a scan parameter so that at least one of a resolution or a pulse energy for the ground portion of the field of regard is modified relative to another portion of the field of regard; and detecting at least a portion of the scanned pulses of light scattered by one or more remote targets.

FIELD OF TECHNOLOGY

This disclosure generally related to lidar systems and, moreparticularly, lidar systems that vary scan parameters when scanning theportion of the field of regard that overlaps the ground.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and an optical receiver. The light source can be, forexample, a laser which emits light having a particular operatingwavelength. The operating wavelength of a lidar system may lie, forexample, in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. The light source emits light toward a targetwhich then scatters the light. Some of the scattered light is receivedback at the receiver. The system determines the distance to the targetbased on one or more characteristics associated with the returned light.For example, the system may determine the distance to the target basedon the time of flight of a returned light pulse.

A typical lidar system is configured to wait for the scattered light toreturn during a certain fixed period of time t_(max) corresponding tothe time it takes a light pulse to travel the maximum distance at whichthe lidar system is configured to detect targets, and back. For example,the lidar system may be configured to detect objects up to 200 metersaway, and t_(max) accordingly can be approximately 1.33 μs. If the lidarsystem does not detect scattered light within t_(max), the lidar systemconcludes that no object was present to scatter the outbound pulse, andgenerates the next light pulse.

SUMMARY

To improve resolution and/or dynamically vary the laser power whencertain properties of the targets are known, a lidar system operating ina terrestrial vehicle (e.g., a car, a truck, an agricultural vehicle)determines where the field of regard of the vehicle overlaps the regionof the ground and adjusts one or more characteristics of the scan forthis portion of the field of regard. More specifically, the lidar systemcan adjust the scan rate and/or the power of outbound light pulses.Changes to resolution can include changes in pixel density along thehorizontal dimension and/or changes in line density (corresponding topixel density along the vertical dimension).

One example embodiment of these techniques is a lidar system comprisinga light source configured to emit pulses of light, a scanner configuredto scan at least a portion of the emitted pulses of light along a scanpattern contained within a field of regard of the lidar system, areceiver configured to detect at least a portion of the scanned pulsesof light scattered by one or more remote targets, and a processor. Thefield of regard includes a ground portion that overlaps a region ofground located ahead of the lidar system. The processor is configured toidentify the ground portion of the field of regard, and, when theemitted pulses scan the ground portion of the field of regard during asubsequent scan of the field of regard, adjust a scan parameter so thatat least one of a resolution or a pulse energy for the ground portion ofthe field of regard is modified relative to another portion of the fieldof regard.

Another example embodiment of these techniques is a method in a lidarsystem for scanning a field of regard of the lidar system. The methodincludes identifying, within the field of regard, a ground portion thatoverlaps a region of ground located ahead of the lidar system; causing alight source to emit pulses of light; scanning at least a portion of theemitted pulses of light along a scan pattern contained within the fieldof regard, including adjusting a scan parameter so that at least one ofa resolution or a pulse energy for the ground portion of the field ofregard is modified relative to another portion of the field of regard;and detecting at least a portion of the scanned pulses of lightscattered by one or more remote targets.

Still another example embodiment of these techniques is an autonomousvehicle comprising vehicle maneuvering components to effectuate at leaststeering, acceleration, and braking of the autonomous vehicle. Theautonomous vehicle further comprises a lidar system including a lightsource configured to emit pulses of light, a scanner configured to scanat least a portion of the emitted pulses of light along a scan patterncontained within a field of regard of the lidar system, where the fieldof regard includes a ground portion that overlaps a region of groundlocated ahead of the lidar system, and a receiver configured to detectat least a portion of the scanned pulses of light scattered by one ormore remote targets. The autonomous vehicle further includes a vehiclecontroller communicatively coupled to the vehicle maneuvering componentsand the lidar system, the vehicle controller configured to control thevehicle maneuvering components using the signals generated by the lidarsystem. The lidar system is configured to, when the emitted pulses scanthe ground portion of the field of regard during a subsequent scan ofthe field of regard, adjust a scan parameter so that at least one of aresolution or a pulse energy for the ground portion of the field ofregard is modified relative to another portion of the field of regard.

Another example embodiment of these techniques is a method in a lidarsystem for determining reflectivity of a certain region within a fieldof regard. The method includes causing a light source to emit pulses oflight and scanning the emitted pulses of light across the field ofregard along a scan pattern. The method further includes determining anamount of emitted light directed toward a region of interest containedwithin the field of regard during a scan, determining an amount of lightscattered by one or more targets disposed in the region of interest, anddetermining a physical property of the region of interest using thedetermined amount of emitted light and the determined amount ofscattered light. In an embodiment, the physical property is an estimateof reflectivity of the region of interest. In an embodiment, the methodfurther includes determining, based on the determining reflectivity,whether the region of interest is a ground region within the field ofregard. In an embodiment, determining the amount of emitted lightincludes determining a total amount of light contained in a plurality ofemitted pulses directed toward the region of interest in accordance withthe scan pattern. In an embodiment, determining the amount of scatteredlight includes determining a total amount of light contained in aplurality of returns corresponding to a plurality of emitted pulsesdirected toward the region of interest in accordance with the scanpattern. Determining the amount of scattered light in some embodimentsin an embodiment includes eliminating statistical outliers from amongthe plurality of returns or absences of returns corresponding to some ofthe emitted pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example light detection and ranging(lidar) system in which the techniques of this disclosure can beimplemented;

FIG. 2 illustrates in more detail several components that can operate inthe system of FIG. 1;

FIG. 3 is a block diagram of lidar system in which the scanner includesa polygon mirror;

FIG. 4 illustrates an example configuration in which the components ofFIG. 1 scan a 360-degree field of regard through a window in a rotatinghousing;

FIG. 5 illustrates another configuration in which the components of FIG.1 scan a 360-degree field of regard through a substantially transparentstationary housing;

FIG. 6 illustrates an example scan pattern which the lidar system ofFIG.1 can produce when identifying targets within a field of regard;

FIG. 7 illustrates an example scan pattern which the lidar system ofFIG.1 can produce when identifying targets within a field of regardusing multiple beams;

FIG. 8 schematically illustrates fields of view (FOVs) of a light sourceand a detector that can operate in the lidar system of FIG. 1;

FIG. 9 illustrates an example configuration of the lidar system of FIG.1 or another suitable lidar system, in which a laser is disposed awayfrom sensor components;

FIG. 10 illustrates an example vehicle in which the lidar system of FIG.1 can operate;

FIG. 11 illustrates an example InGaAs avalanche photodiode which canoperate in the lidar system of FIG. 1;

FIG. 12 illustrates an example photodiode coupled to a pulse-detectioncircuit, which can operate in the lidar system of FIG. 1;

FIG. 13 illustrates an example light source that includes a seed laserand an amplifier, which can operate in the lidar system of FIG. 1;

FIG. 14 illustrates an example implementation of the amplifier of FIG.13;

FIG. 15 illustrates an example scene within a field of regard of thelidar system of FIG. 1 operating in a vehicle, where the field of regardoverlaps a region of ground ahead of the vehicle;

FIG. 16 is a flow diagram of an example method for adjusting one or morescan parameters to increase resolution and/or modify pulse power whenscanning the ground ahead of the vehicle;

FIG. 17 illustrates detection of the ground portion of the field ofregard when the vehicle in which the lidar system operates is travellingon a road with a downward slope;

FIG. 18 illustrates detection of the ground portion in the field ofregard when the vehicle in which the lidar system operates is travellingon a road with an upward slope;

FIG. 19 illustrates an example scan pattern with an increased linedensity in the ground portion in the field of regard;

FIG. 20 illustrates an example scan pattern with an increased horizontalresolution in the ground portion of the field of regard;

FIG. 21 illustrates another example selection of one or more scanparameters for scanning the ground portion of the field of regard; and

FIG. 22 is a timing diagram of an example technique for transmittinglight pulses upon detection of return pulses, which can be implementedin the lidar system of this disclosure.

DETAILED DESCRIPTION Overview

A lidar system configured to operate in a terrestrial vehicledetermines, based on the data previously collected by the lidar systemor an indication from another sensor, where the field of regard of thelidar system overlaps a region of ground located ahead of the lidarsystem (“the ground region”), and adjusts one or more scan parametersfor the scan of the corresponding portion of the field of regard (“theground portion”).

In some cases, the lidar system determines the ground portion of thefield of regard using the data collected during the previous scan orscans of the field of regard. The lidar system also can use data from acamera (e.g., a CCD or CMOS camera), an acoustic array, or anothersuitable sensor or a combination of sensors. Further, the lidar systemcan use positioning data along with topographical data from a GIS system(pre-stored or received via a communication network for the relevantlocation), and further in view of where the lidar system is mounted inthe vehicle.

The one or more scan parameters the lidar system can modify include scanline density, horizontal resolution, pixel density, pulse rate or pulserepetition frequency, pulse energy, etc. The lidar system can vary thesescan parameters by modifying the operation of the light source and/orthe scanner, for example. By adjusting one or more scan parameters forthe ground portion of the field of regard, the lidar system can producea high-resolution scan of a portion of the field of regard and/or a moreefficient distribution of laser power across the field of regard.

The lidar system thus can provide additional horizontal resolution formany driving scenarios where it is desirable. For example, when scanningthe road, additional horizontal resolution is helpful in identifyingroad markers, lanes, potholes, retroreflectors, or other objects locatedon or associated with the road. The lidar system also can provideadditional laser power in those driving scenarios when additional laserpower is desirable. For example, when the lidar system emits a lightpulse that strikes the road at a low enough grazing angle (aka, aglancing angle), the light pulse is reflected by the road and verylittle light is scattered.

Example Lidar System

FIG. 1 illustrates an example light detection and ranging (lidar) system100. The lidar system 100 may be referred to as a laser ranging system,a laser radar system, a LIDAR system, a lidar sensor, or a laserdetection and ranging (LADAR or ladar) system. The lidar system 100 mayinclude a light source 110, an optical coupling component 113 includinga mirror 115, a scanner 120, a receiver 140, and a controller 150. Thelight source 110 may be, for example, a laser which emits light having aparticular operating wavelength in the infrared, visible, or ultravioletportions of the electromagnetic spectrum. As a more specific example,the light source 110 may include a laser with an operating wavelengthbetween approximately 1.2 μm and 1.7 μm.

In operation, the light source 110 emits an output beam of light 125which may be continuous-wave (CW), pulsed, or modulated in any suitablemanner for a given application. In this disclosure, the emitted lightcan be described as a pulse of light. In some implementations, the pulsemay have a duration as long as the time interval until the next emittedpulse. In some implementations, the pulse may exhibit a variation inlight intensity and/or a variation in light frequency throughout theduration of the pulse. Thus, for example, in a frequency-modulated CW(FMCW) lidar system, a pulse may be defined by a full cycle of themodulated frequency, even when the intensity stays constant within thepulse or from one pulse to another. The output beam of light 125 isdirected downrange toward a remote target 130 located a distance D fromthe lidar system 100 and at least partially contained within a field ofregard of the system 100. Depending on the scenario and/or theimplementation of the lidar system 100, D can be between 1 m and 1 km,for example.

Once the output beam 125 reaches the downrange target 130, the target130 may scatter or, in some cases, reflect at least a portion of lightfrom the output beam 125, and some of the scattered or reflected lightmay return toward the lidar system 100. In the example of FIG. 1, thescattered or reflected light is represented by input beam 135, whichpasses through the scanner 120, which may be referred to as a beamscanner, optical scanner, or laser scanner. The input beam 135 passesthrough the scanner 120 to the mirror 115, which may be referred to asan overlap mirror, superposition mirror, or beam-combiner mirror. Themirror 115 in turn directs the input beam 135 to the receiver 140. Theinput beam 135 may contain only a relatively small fraction of the lightfrom the output beam 125. For example, the ratio of average power, peakpower, or pulse energy of the input beam 135 to average power, peakpower, or pulse energy of the output beam 125 may be approximately 10⁻¹,10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹, 10⁻¹⁰, 10⁻¹¹, or 10⁻¹².As another example, if a pulse of the output beam 125 has a pulse energyof 1 microjoule (μJ), then the pulse energy of a corresponding pulse ofthe input beam 135 may have a pulse energy of approximately 10nanojoules (nJ), 1 nJ, 100 picojoules (pJ), 10 pJ, 1 pJ, 100 femtojoules(fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10 aJ, or 1 aJ.

The output beam 125 may be referred to as a laser beam, light beam,optical beam, emitted beam, or just beam; and the input beam 135 may bereferred to as a return beam, received beam, return light, receivedlight, input light, scattered light, or reflected light. As used herein,scattered light may refer to light that is scattered or reflected by thetarget 130. The input beam 135 may include light from the output beam125 that is scattered by the target 130, light from the output beam 125that is reflected by the target 130, or a combination of scattered andreflected light from target 130.

The operating wavelength of a lidar system 100 may lie, for example, inthe infrared, visible, or ultraviolet portions of the electromagneticspectrum. The Sun also produces light in these wavelength ranges, andthus sunlight can act as background noise which can obscure signal lightdetected by the lidar system 100. This solar background noise can resultin false-positive detections or can otherwise corrupt measurements ofthe lidar system 100, especially when the receiver 140 includes SPADdetectors (which can be highly sensitive).

Generally speaking, the light from the Sun that passes through theEarth's atmosphere and reaches a terrestrial-based lidar system such asthe system 100 can establish an optical background noise floor for thissystem. Thus, in order for a signal from the lidar system 100 to bedetectable, the signal must rise above the background noise floor. It isgenerally possible to increase the signal-to-noise (SNR) ratio of thelidar system 100 by raising the power level of the output beam 125, butin some situations it may be desirable to keep the power level of theoutput beam 125 relatively low. For example, increasing transmit powerlevels of the output beam 125 can result in the lidar system 100 notbeing eye-safe.

In some implementations, the lidar system 100 operates at one or morewavelengths between approximately 1400 nm and approximately 1600 nm. Forexample, the light source 110 may produce light at approximately 1550nm.

In some implementations, the lidar system 100 operates at frequencies atwhich atmospheric absorption is relatively low. For example, the lidarsystem 100 can operate at wavelengths in the approximate ranges from 980nm to 1110 nm or from 1165 nm to 1400 nm.

In other implementations, the lidar system 100 operates at frequenciesat which atmospheric absorption is high. For example, the lidar system100 can operate at wavelengths in the approximate ranges from 930 nm to980 nm, from 1100 nm to 1165 nm, or from 1400 nm to 1460 nm.

According to some implementations, the lidar system 100 can include aneye-safe laser, or the lidar system 100 can be classified as an eye-safelaser system or laser product. An eye-safe laser, laser system, or laserproduct may refer to a system with an emission wavelength, averagepower, peak power, peak intensity, pulse energy, beam size, beamdivergence, exposure time, or scanned output beam such that emittedlight from the system presents little or no possibility of causingdamage to a person's eyes. For example, the light source 110 or lidarsystem 100 may be classified as a Class 1 laser product (as specified bythe 60825-1 standard of the International Electrotechnical Commission(IEC)) or a Class I laser product (as specified by Title 21, Section1040.10 of the United States Code of Federal Regulations (CFR)) that issafe under all conditions of normal use. In some implementations, thelidar system 100 may be classified as an eye-safe laser product (e.g.,with a Class 1 or Class I classification) configured to operate at anysuitable wavelength between approximately 1400 nm and approximately 2100nm. In some implementations, the light source 110 may include a laserwith an operating wavelength between approximately 1400 nm andapproximately 1600 nm, and the lidar system 100 may be operated in aneye-safe manner. In some implementations, the light source 110 or thelidar system 100 may be an eye-safe laser product that includes ascanned laser with an operating wavelength between approximately 1530 nmand approximately 1560 nm. In some implementations, the lidar system 100may be a Class 1 or Class I laser product that includes a fiber laser orsolid-state laser with an operating wavelength between approximately1400 nm and approximately 1600 nm.

The receiver 140 may receive or detect photons from the input beam 135and generate one or more representative signals. For example, thereceiver 140 may generate an output electrical signal 145 that isrepresentative of the input beam 135. The receiver may send theelectrical signal 145 to the controller 150. Depending on theimplementation, the controller 150 may include one or more processors,an application-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), and/or other suitable circuitry configured to analyzeone or more characteristics of the electrical signal 145 to determineone or more characteristics of the target 130, such as its distancedownrange from the lidar system 100. More particularly, the controller150 may analyze the time of flight or phase modulation for the beam oflight 125 transmitted by the light source 110. If the lidar system 100measures a time of flight of T (e.g., T represents a round-trip time offlight for an emitted pulse of light to travel from the lidar system 100to the target 130 and back to the lidar system 100), then the distance Dfrom the target 130 to the lidar system 100 may be expressed as D=c·T/2,where c is the speed of light (approximately 3.0×10⁸ m/s).

As a more specific example, if the lidar system 100 measures the time offlight to be T=300 ns, then the lidar system 100 can determine thedistance from the target 130 to the lidar system 100 to be approximatelyD=45.0 m. As another example, the lidar system 100 measures the time offlight to be T=1.33 μs and accordingly determines that the distance fromthe target 130 to the lidar system 100 is approximately D=199.5 m. Thedistance D from lidar system 100 to the target 130 may be referred to asa distance, depth, or range of the target 130. As used herein, the speedof light c refers to the speed of light in any suitable medium, such asfor example in air, water, or vacuum. The speed of light in vacuum isapproximately 2.9979×10⁸ m/s, and the speed of light in air (which has arefractive index of approximately 1.0003) is approximately 2.9970×10⁸m/s.

The target 130 may be located a distance D from the lidar system 100that is less than or equal to a maximum range R_(MAX) of the lidarsystem 100. The maximum range R_(MAX) (which also may be referred to asa maximum distance) of a lidar system 100 may correspond to the maximumdistance over which the lidar system 100 is configured to sense oridentify targets that appear in a field of regard of the lidar system100. The maximum range of lidar system 100 may be any suitable distance,such as for example, 25 m, 50 m, 100 m, 200 m, 500 m, or 1 km. As aspecific example, a lidar system with a 200-m maximum range may beconfigured to sense or identify various targets located up to 200 maway. For a lidar system with a 200-m maximum range (R_(MAX)=200 m), thetime of flight corresponding to the maximum range is approximately2·R_(MAX)/c≅1.33 μs.

In some implementations, the light source 110, the scanner 120, and thereceiver 140 may be packaged together within a single housing 155, whichmay be a box, case, or enclosure that holds or contains all or part of alidar system 100. The housing 155 includes a window 157 through whichthe beams 125 and 135 pass. In one example implementation, thelidar-system housing 155 contains the light source 110, the overlapmirror 115, the scanner 120, and the receiver 140 of a lidar system 100.The controller 150 may reside within the same housing 155 as thecomponents 110, 120, and 140, or the controller 150 may reside remotelyfrom the housing.

Moreover, in some implementations, the housing 155 includes multiplelidar sensors, each including a respective scanner and a receiver.Depending on the particular implementation, each of the multiple sensorscan include a separate light source or a common light source. Themultiple sensors can be configured to cover non-overlapping adjacentfields of regard or partially overlapping fields of regard, depending onthe implementation.

The housing 155 may be an airtight or watertight structure that preventswater vapor, liquid water, dirt, dust, or other contaminants fromgetting inside the housing 155. The housing 155 may be filled with a dryor inert gas, such as for example dry air, nitrogen, or argon. Thehousing 155 may include one or more electrical connections for conveyingelectrical power or electrical signals to and/or from the housing.

The window 157 may be made from any suitable substrate material, such asfor example, glass or plastic (e.g., polycarbonate, acrylic,cyclic-olefin polymer, or cyclic-olefin copolymer). The window 157 mayinclude an interior surface (surface A) and an exterior surface (surfaceB), and surface A or surface B may include a dielectric coating havingparticular reflectivity values at particular wavelengths. A dielectriccoating (which may be referred to as a thin-film coating, interferencecoating, or coating) may include one or more thin-film layers ofdielectric materials (e.g., SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃, orAlF₃) having particular thicknesses (e.g., thickness less than 1 μm) andparticular refractive indices. A dielectric coating may be depositedonto surface A or surface B of the window 157 using any suitabledeposition technique, such as for example, sputtering or electron-beamdeposition.

The dielectric coating may have a high reflectivity at a particularwavelength or a low reflectivity at a particular wavelength. Ahigh-reflectivity (HR) dielectric coating may have any suitablereflectivity value (e.g., a reflectivity greater than or equal to 80%,90%, 95%, or 99%) at any suitable wavelength or combination ofwavelengths. A low-reflectivity dielectric coating (which may bereferred to as an anti-reflection (AR) coating) may have any suitablereflectivity value (e.g., a reflectivity less than or equal to 5%, 2%,1%, 0.5%, or 0.2%) at any suitable wavelength or combination ofwavelengths. In particular embodiments, a dielectric coating may be adichroic coating with a particular combination of high or lowreflectivity values at particular wavelengths. For example, a dichroiccoating may have a reflectivity of less than or equal to 0.5% atapproximately 1550-1560 nm and a reflectivity of greater than or equalto 90% at approximately 800-1500 nm.

In some implementations, surface A or surface B has a dielectric coatingthat is anti-reflecting at an operating wavelength of one or more lightsources 110 contained within enclosure 155. An AR coating on surface Aand surface B may increase the amount of light at an operatingwavelength of light source 110 that is transmitted through the window157. Additionally, an AR coating at an operating wavelength of the lightsource 110 may reduce the amount of incident light from output beam 125that is reflected by the window 157 back into the housing 155. In anexample implementation, each of surface A and surface B has an ARcoating with reflectivity less than 0.5% at an operating wavelength oflight source 110. As an example, if the light source 110 has anoperating wavelength of approximately 1550 nm, then surface A andsurface B may each have an AR coating with a reflectivity that is lessthan 0.5% from approximately 1547 nm to approximately 1553 nm. Inanother implementation, each of surface A and surface B has an ARcoating with reflectivity less than 1% at the operating wavelengths ofthe light source 110. For example, if the housing 155 encloses twosensor heads with respective light sources, the first light source emitspulses at a wavelength of approximately 1535 nm and the second lightsource emits pulses at a wavelength of approximately 1540 nm, thensurface A and surface B may each have an AR coating with reflectivityless than 1% from approximately 1530 nm to approximately 1545 nm.

The window 157 may have an optical transmission that is greater than anysuitable value for one or more wavelengths of one or more light sources110 contained within the housing 155. As an example, the window 157 mayhave an optical transmission of greater than or equal to 70%, 80%, 90%,95%, or 99% at a wavelength of light source 110. In one exampleimplementation, the window 157 can transmit greater than or equal to 95%of light at an operating wavelength of the light source 110. In anotherimplementation, the window 157 transmits greater than or equal to 90% oflight at the operating wavelengths of the light sources enclosed withinthe housing 155.

Surface A or surface B may have a dichroic coating that isanti-reflecting at one or more operating wavelengths of one or morelight sources 110 and high-reflecting at wavelengths away from the oneor more operating wavelengths. For example, surface A may have an ARcoating for an operating wavelength of the light source 110, and surfaceB may have a dichroic coating that is AR at the light-source operatingwavelength and HR for wavelengths away from the operating wavelength. Acoating that is HR for wavelengths away from a light-source operatingwavelength may prevent most incoming light at unwanted wavelengths frombeing transmitted through the window 117. In one implementation, iflight source 110 emits optical pulses with a wavelength of approximately1550 nm, then surface A may have an AR coating with a reflectivity ofless than or equal to 0.5% from approximately 1546 nm to approximately1554 nm. Additionally, surface B may have a dichroic coating that is ARat approximately 1546-1554 nm and HR (e.g., reflectivity of greater thanor equal to 90%) at approximately 800-1500 nm and approximately1580-1700 nm.

Surface B of the window 157 may include a coating that is oleophobic,hydrophobic, or hydrophilic. A coating that is oleophobic (or,lipophobic) may repel oils (e.g., fingerprint oil or other non-polarmaterial) from the exterior surface (surface B) of the window 157. Acoating that is hydrophobic may repel water from the exterior surface.For example, surface B may be coated with a material that is botholeophobic and hydrophobic. A coating that is hydrophilic attracts waterso that water may tend to wet and form a film on the hydrophilic surface(rather than forming beads of water as may occur on a hydrophobicsurface). If surface B has a hydrophilic coating, then water (e.g., fromrain) that lands on surface B may form a film on the surface. Thesurface film of water may result in less distortion, deflection, orocclusion of an output beam 125 than a surface with a non-hydrophiliccoating or a hydrophobic coating.

With continued reference to FIG. 1, the light source 110 may include apulsed laser configured to produce or emit pulses of light with acertain pulse duration. In an example implementation, the pulse durationor pulse width of the pulsed laser is approximately 10 picoseconds (ps)to 100 nanoseconds (ns). In another implementation, the light source 110is a pulsed laser that produces pulses with a pulse duration ofapproximately 1-4 ns. In yet another implementation, the light source110 is a pulsed laser that produces pulses at a pulse repetitionfrequency of approximately 100 kHz to 5 MHz or a pulse period (e.g., atime between consecutive pulses) of approximately 200 ns to 10 μs. Thelight source 110 may have a substantially constant or a variable pulserepetition frequency, depending on the implementation. As an example,the light source 110 may be a pulsed laser that produces pulses at asubstantially constant pulse repetition frequency of approximately 640kHz (e.g., 640,000 pulses per second), corresponding to a pulse periodof approximately 1.56 μs. As another example, the light source 110 mayhave a pulse repetition frequency that can be varied from approximately500 kHz to 3 MHz. As used herein, a pulse of light may be referred to asan optical pulse, a light pulse, or a pulse, and a pulse repetitionfrequency may be referred to as a pulse rate.

In general, the output beam 125 may have any suitable average opticalpower, and the output beam 125 may include optical pulses with anysuitable pulse energy or peak optical power. Some examples of theaverage power of the output beam 125 include the approximate values of 1mW, 10 mW, 100 mW, 1 W, and 10 W. Example values of pulse energy of theoutput beam 125 include the approximate values of 0.1 μJ, 1 μJ, 10 μJ,100 μJ, and 1 mJ. Examples of peak power values of pulses included inthe output beam 125 are the approximate values of 10 W, 100 W, 1 kW, 5kW, 10 kW. An example optical pulse with a duration of 1 ns and a pulseenergy of 1 μJ has a peak power of approximately 1 kW. If the pulserepetition frequency is 500 kHz, then the average power of the outputbeam 125 with 1-μJ pulses is approximately 0.5 W, in this example.

The light source 110 may include a laser diode, such as a Fabry-Perotlaser diode, a quantum well laser, a distributed Bragg reflector (DBR)laser, a distributed feedback (DFB) laser, or a vertical-cavitysurface-emitting laser (VCSEL). The laser diode operating in the lightsource 110 may be an aluminum-gallium-arsenide (AlGaAs) laser diode, anindium-gallium-arsenide (InGaAs) laser diode, or anindium-gallium-arsenide-phosphide (InGaAsP) laser diode, or any othersuitable diode. In some implementations, the light source 110 includes apulsed laser diode with a peak emission wavelength of approximately1400-1600 nm. Further, the light source 110 may include a laser diodethat is current-modulated to produce optical pulses.

In some implementations, the light source 110 includes a pulsed laserdiode followed by one or more optical-amplification stages. For example,the light source 110 may be a fiber-laser module that includes acurrent-modulated laser diode with a peak wavelength of approximately1550 nm, followed by a single-stage or a multi-stage erbium-doped fiberamplifier (EDFA). As another example, the light source 110 may include acontinuous-wave (CW) or quasi-CW laser diode followed by an externaloptical modulator (e.g., an electro-optic modulator), and the output ofthe modulator may be fed into an optical amplifier. In otherimplementations, the light source 110 may include a laser diode whichproduces optical pulses that are not amplified by an optical amplifier.As an example, a laser diode (which may be referred to as a directemitter or a direct-emitter laser diode) may emit optical pulses thatform an output beam 125 that is directed downrange from a lidar system100. In yet other implementations, the light source 110 may include apulsed solid-state laser or a pulsed fiber laser.

Although this disclosure describes or illustrates example embodiments oflidar systems or light sources that produce light waveforms that includepulses of light, the embodiments described or illustrated herein mayalso be applied to other types of light waveforms, includingcontinuous-wave (CW) light or modulated light waveforms. For example, alidar system as described or illustrated herein may include a lightsource configured to produce pulses of light. Alternatively, a lidarsystem may be configured to act as a frequency-modulated continuous-wave(FMCW) lidar system and may include a light source configured to produceCW light or a frequency-modulated light waveform.

A pulsed lidar system is one type of lidar system in which the lightsource emits pulses of light, and the distance to a remote target isdetermined from the time-of-flight for a pulse of light to travel to thetarget and back. Another type of lidar system is a frequency-modulatedlidar system, which may be referred to as a frequency-modulatedcontinuous-wave (FMCW) lidar system. A FMCW lidar system usesfrequency-modulated light to determine the distance to a remote targetbased on a modulation frequency of the received light (which isscattered from a remote target) relative to the modulation frequency ofthe emitted light. For example, for a linearly chirped light source(e.g., a frequency modulation that produces a linear change in frequencywith time), the larger the frequency difference between the emittedlight and the received light, the farther away the target is located.The frequency difference can be determined by mixing the received lightwith a portion of the emitted light (e.g., by coupling the two beamsonto a detector, or mixing analog electric signals corresponding to thereceived light and the emitted light) and determining the resulting beatfrequency. For example, the electrical signal from an APD can beanalyzed using a fast Fourier transform (FFT) technique to determine thefrequency difference between the emitted light and the received light.

If a linear frequency modulation m (e.g., in units of Hz/s) is appliedto a CW laser, then the distance D from the target to the lidar systemmay be expressed as D=c·Δf/(2 m), where c is the speed of light and Δfis the difference in frequency between the transmitted light and thereceived light. For example, for a linear frequency modulation of 10¹²Hz/s (or, 1 MHz/μs), if a frequency difference of 330 kHz is measured,then the distance to the target is approximately 50 meters.Additionally, a frequency difference of 1.33 MHz corresponds to a targetlocated approximately 200 meters away.

The light source for a FMCW lidar system can be a fiber laser (e.g., aseed laser diode followed by one or more optical amplifiers) or adirect-emitter laser diode. The seed laser diode or the direct-emitterlaser diode can be operated in a CW manner (e.g., by driving the laserdiode with a substantially constant DC current), and the frequencymodulation can be provided by an external modulator (e.g., anelectro-optic phase modulator). Alternatively, the frequency modulationcan be produced by applying a DC bias current along with a currentmodulation to the seed laser diode or the direct-emitter laser diode.The current modulation produces a corresponding refractive-indexmodulation in the laser diode, which results in a frequency modulationof the light emitted by the laser diode. The current-modulationcomponent (and corresponding frequency modulation) can have any suitablefrequency or shape (e.g., piecewise linear, sinusoidal, triangle-wave,or sawtooth).

In some implementations, the output beam of light 125 emitted by thelight source 110 is a collimated optical beam with any suitable beamdivergence, such as a divergence of approximately 0.1 to 3.0 milliradian(mrad). Divergence of the output beam 125 may refer to an angularmeasure of an increase in beam size (e.g., a beam radius or beamdiameter) as the output beam 125 travels away from the light source 110or the lidar system 100. The output beam 125 may have a substantiallycircular cross section with a beam divergence characterized by a singledivergence value. For example, the output beam 125 with a circular crosssection and a divergence of 1 mrad may have a beam diameter or spot sizeof approximately 10 cm at a distance of 100 m from the lidar system 100.In some implementations, the output beam 125 may be an astigmatic beamor may have a substantially elliptical cross section and may becharacterized by two divergence values. As an example, the output beam125 may have a fast axis and a slow axis, where the fast-axis divergenceis greater than the slow-axis divergence. As another example, the outputbeam 125 may be an astigmatic beam with a fast-axis divergence of 2 mradand a slow-axis divergence of 0.5 mrad.

The output beam of light 125 emitted by light source 110 may beunpolarized or randomly polarized, may have no specific or fixedpolarization (e.g., the polarization may vary with time), or may have aparticular polarization (e.g., the output beam 125 may be linearlypolarized, elliptically polarized, or circularly polarized). As anexample, the light source 110 may produce linearly polarized light, andthe lidar system 100 may include a quarter-wave plate that converts thislinearly polarized light into circularly polarized light. The lidarsystem 100 may transmit the circularly polarized light as the outputbeam 125, and receive the input beam 135, which may be substantially orat least partially circularly polarized in the same manner as the outputbeam 125 (e.g., if the output beam 125 is right-hand circularlypolarized, then the input beam 135 may also be right-hand circularlypolarized). The input beam 135 may pass through the same quarter-waveplate (or a different quarter-wave plate), resulting in the input beam135 being converted to linearly polarized light which is orthogonallypolarized (e.g., polarized at a right angle) with respect to thelinearly polarized light produced by light source 110. As anotherexample, the lidar system 100 may employ polarization-diversitydetection where two polarization components are detected separately. Theoutput beam 125 may be linearly polarized, and the lidar system 100 maysplit the input beam 135 into two polarization components (e.g.,s-polarization and p-polarization) which are detected separately by twophotodiodes (e.g., a balanced photoreceiver that includes twophotodiodes).

With continued reference to FIG. 1, the output beam 125 and input beam135 may be substantially coaxial. In other words, the output beam 125and input beam 135 may at least partially overlap or share a commonpropagation axis, so that the input beam 135 and the output beam 125travel along substantially the same optical path (albeit in oppositedirections). As the lidar system 100 scans the output beam 125 across afield of regard, the input beam 135 may follow along with the outputbeam 125, so that the coaxial relationship between the two beams ismaintained.

The lidar system 100 also may include one or more optical componentsconfigured to condition, shape, filter, modify, steer, or direct theoutput beam 125 and/or the input beam 135. For example, lidar system 100may include one or more lenses, mirrors, filters (e.g., bandpass orinterference filters), beam splitters, polarizers, polarizing beamsplitters, wave plates (e.g., half-wave or quarter-wave plates),diffractive elements, or holographic elements. In some implementations,lidar system 100 includes a telescope, one or more lenses, or one ormore mirrors to expand, focus, or collimate the output beam 125 to adesired beam diameter or divergence. As an example, the lidar system 100may include one or more lenses to focus the input beam 135 onto anactive region of the receiver 140. As another example, the lidar system100 may include one or more flat mirrors or curved mirrors (e.g.,concave, convex, or parabolic mirrors) to steer or focus the output beam125 or the input beam 135. For example, the lidar system 100 may includean off-axis parabolic mirror to focus the input beam 135 onto an activeregion of receiver 140. As illustrated in FIG. 1, the lidar system 100may include the mirror 115, which may be a metallic or dielectricmirror. The mirror 115 may be configured so that the light beam 125passes through the mirror 115. As an example, the mirror 115 may includea hole, slot, or aperture through which the output light beam 125passes. As another example, the mirror 115 may be configured so that atleast 80% of the output beam 125 passes through the mirror 115 and atleast 80% of the input beam 135 is reflected by the mirror 115. In someimplementations, the mirror 115 may provide for the output beam 125 andthe input beam 135 to be substantially coaxial, so that the beams 125and 135 travel along substantially the same optical path, in oppositedirections.

Although the component 113 in this example implementation includes theoverlap mirror 115 through which the output beam 125 travels from thelight source 110 toward the scanner 120, in general the component 113can include a mirror without an aperture so that the output beam 125travels past the mirror 115 in accordance with off-axis illuminationtechnique, for example. More generally, the component 113 can includeany suitable optical elements to direct the output beam 125 toward thescanner 120 and the input beam 135 toward the receiver 140.

Generally speaking, the scanner 120 steers the output beam 125 in one ormore directions downrange. The scanner 120 may include one or morescanning mirrors and one or more actuators driving the mirrors torotate, tilt, pivot, or move the mirrors in an angular manner about oneor more axes, for example. For example, the first mirror of the scannermay scan the output beam 125 along a first direction, and the secondmirror may scan the output beam 125 along a second direction that issubstantially orthogonal to the first direction. Example implementationsof the scanner 120 are discussed in more detail below with reference toFIG. 2.

The scanner 120 may be configured to scan the output beam 125 over a5-degree angular range, 20-degree angular range, 30-degree angularrange, 60-degree angular range, or any other suitable angular range. Forexample, a scanning mirror may be configured to periodically rotate overa 15-degree range, which results in the output beam 125 scanning acrossa 30-degree range (e.g., a Θ-degree rotation by a scanning mirrorresults in a 2Θ-degree angular scan of the output beam 125). A field ofregard (FOR) of the lidar system 100 may refer to an area, region, orangular range over which the lidar system 100 may be configured to scanor capture distance information. When the lidar system 100 scans theoutput beam 125 within a 30-degree scanning range, the lidar system 100may be referred to as having a 30-degree angular field of regard. Asanother example, a lidar system 100 with a scanning mirror that rotatesover a 30-degree range may produce the output beam 125 that scans acrossa 60-degree range (e.g., a 60-degree FOR). In various implementations,the lidar system 100 may have a FOR of approximately 10°, 20°, 40°, 60°,120°, or any other suitable FOR. The FOR also may be referred to as ascan region.

The scanner 120 may be configured to scan the output beam 125horizontally and vertically, and the lidar system 100 may have aparticular FOR along the horizontal direction and another particular FORalong the vertical direction. For example, the lidar system 100 may havea horizontal FOR of 10° to 120° and a vertical FOR of 2° to 45°.

The one or more scanning mirrors of the scanner 120 may becommunicatively coupled to the controller 150 which may control thescanning mirror(s) so as to guide the output beam 125 in a desireddirection downrange or along a desired scan pattern. In general, a scanpattern may refer to a pattern or path along which the output beam 125is directed, and also may be referred to as an optical scan pattern,optical scan path, or scan path. As an example, the scanner 120 mayinclude two scanning mirrors configured to scan the output beam 125across a 60° horizontal FOR and a 20° vertical FOR. The two scannermirrors may be controlled to follow a scan path that substantiallycovers the 60°×20° FOR. The lidar system 100 can use the scan path togenerate a point cloud with pixels that substantially cover the 60°×20°FOR. The pixels may be approximately evenly distributed across the60°×20° FOR. Alternately, the pixels may have a particular non-uniformdistribution (e.g., the pixels may be distributed across all or aportion of the 60°×20° FOR, and the pixels may have a higher density inone or more particular regions of the 60°×20° FOR).

In operation, the light source 110 may emit pulses of light which thescanner 120 scans across a FOR of lidar system 100. The target 130 mayscatter one or more of the emitted pulses, and the receiver 140 maydetect at least a portion of the pulses of light scattered by the target130.

The receiver 140 may be referred to as (or may include) a photoreceiver,optical receiver, optical sensor, detector, photodetector, or opticaldetector. The receiver 140 in some implementations receives or detectsat least a portion of the input beam 135 and produces an electricalsignal that corresponds to the input beam 135. For example, if the inputbeam 135 includes an optical pulse, then the receiver 140 may produce anelectrical current or voltage pulse that corresponds to the opticalpulse detected by the receiver 140. In an example implementation, thereceiver 140 includes one or more avalanche photodiodes (APDs) or one ormore single-photon avalanche diodes (SPADs). In another implementation,the receiver 140 includes one or more PN photodiodes (e.g., a photodiodestructure formed by a p-type semiconductor and a n-type semiconductor)or one or more PIN photodiodes (e.g., a photodiode structure formed byan undoped intrinsic semiconductor region located between p-type andn-type regions).

The receiver 140 may have an active region or anavalanche-multiplication region that includes silicon, germanium, orInGaAs. The active region of receiver 140 may have any suitable size,such as for example, a diameter or width of approximately 50-500 μm. Thereceiver 140 may include circuitry that performs signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. For example, thereceiver 140 may include a transimpedance amplifier that converts areceived photocurrent (e.g., a current produced by an APD in response toa received optical signal) into a voltage signal. The receiver 140 maydirect the voltage signal to pulse-detection circuitry that produces ananalog or digital output signal 145 that corresponds to one or morecharacteristics (e.g., rising edge, falling edge, amplitude, orduration) of a received optical pulse. For example, the pulse-detectioncircuitry may perform a time-to-digital conversion to produce a digitaloutput signal 145. The receiver 140 may send the electrical outputsignal 145 to the controller 150 for processing or analysis, e.g., todetermine a time-of-flight value corresponding to a received opticalpulse.

The controller 150 may be electrically coupled or otherwisecommunicatively coupled to one or more of the light source 110, thescanner 120, and the receiver 140. The controller 150 may receiveelectrical trigger pulses or edges from the light source 110, where eachpulse or edge corresponds to the emission of an optical pulse by thelight source 110. The controller 150 may provide instructions, a controlsignal, or a trigger signal to the light source 110 indicating when thelight source 110 should produce optical pulses. For example, thecontroller 150 may send an electrical trigger signal that includeselectrical pulses, where the light source 110 emits an optical pulse inresponse to each electrical pulse. Further, the controller 150 may causethe light source 110 to adjust one or more of the frequency, period,duration, pulse energy, peak power, average power, or wavelength of theoptical pulses produced by light source 110.

The controller 150 may determine a time-of-flight value for an opticalpulse based on timing information associated with when the pulse wasemitted by light source 110 and when a portion of the pulse (e.g., theinput beam 135) was detected or received by the receiver 140. Thecontroller 150 may include circuitry that performs signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection.

The controller 150 also can receive signals from one or more sensors158, which in various implementations are internal to the lidar system100 or, as illustrated in FIG. 1, external to the lidar system 100. Theone or more sensors 158 can include a camera, such as a CCD or CMOSdigital camera, microphone or a microphone array, a radar, etc. In someimplementations, the lidar system 100 uses signals from the one or moresensors 158 to determine which portion of the field of regard overlapsthe ground in front of the lidar system.

As indicated above, the lidar system 100 may be used to determine thedistance to one or more downrange targets 130. By scanning the lidarsystem 100 across a field of regard, the system can be used to map thedistance to a number of points within the field of regard. Each of thesedepth-mapped points may be referred to as a pixel or a voxel. Acollection of pixels captured in succession (which may be referred to asa depth map, a point cloud, or a frame) may be rendered as an image ormay be analyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. For example, a depth map may cover afield of regard that extends 60° horizontally and 15° vertically, andthe depth map may include a frame of 100-2000 pixels in the horizontaldirection by 4-400 pixels in the vertical direction.

The lidar system 100 may be configured to repeatedly capture or generatepoint clouds of a field of regard at any suitable frame rate betweenapproximately 0.1 frames per second (FPS) and approximately 1,000 FPS.For example, the lidar system 100 may generate point clouds at a framerate of approximately 0.1 FPS, 0.5 FPS, 1 FPS, 2 FPS, 5 FPS, 10 FPS, 20FPS, 100 FPS, 500 FPS, or 1,000 FPS. In an example implementation, thelidar system 100 is configured to produce optical pulses at a rate of5×10⁵ pulses/second (e.g., the system may determine 500,000 pixeldistances per second) and scan a frame of 1000×50 pixels (e.g., 50,000pixels/frame), which corresponds to a point-cloud frame rate of 10frames per second (e.g., 10 point clouds per second). The point-cloudframe rate may be substantially fixed or dynamically adjustable,depending on the implementation. For example, the lidar system 100 maycapture one or more point clouds at a particular frame rate (e.g., 1 Hz)and then switch to capture one or more point clouds at a different framerate (e.g., 10 Hz). In general, the lidar system can use a slower framerate (e.g., 1 Hz) to capture one or more high-resolution point clouds,and use a faster frame rate (e.g., 10 Hz) to rapidly capture multiplelower-resolution point clouds.

The field of regard of the lidar system 100 can overlap, encompass, orenclose at least a portion of the target 130, which may include all orpart of an object that is moving or stationary relative to lidar system100. For example, the target 130 may include all or a portion of aperson, vehicle, motorcycle, truck, train, bicycle, wheelchair,pedestrian, animal, road sign, traffic light, lane marking, road-surfacemarking, parking space, pylon, guard rail, traffic barrier, pothole,railroad crossing, obstacle in or near a road, curb, stopped vehicle onor beside a road, utility pole, house, building, trash can, mailbox,tree, any other suitable object, or any suitable combination of all orpart of two or more objects.

Now referring to FIG. 2, a scanner 162 and a receiver 164 can operate inthe lidar system of FIG. 1 as the scanner 120 and the receiver 140,respectively. More generally, the scanner 162 and the receiver 164 canoperate in any suitable lidar system.

The scanner 162 may include any suitable number of mirrors driven by anysuitable number of mechanical actuators. For example, the scanner 162may include a galvanometer scanner, a resonant scanner, a piezoelectricactuator, a polygonal scanner, a rotating-prism scanner, a voice coilmotor, a DC motor, a brushless DC motor, a stepper motor, or amicroelectromechanical systems (MEMS) device, or any other suitableactuator or mechanism.

A galvanometer scanner (which also may be referred to as a galvanometeractuator) may include a galvanometer-based scanning motor with a magnetand coil. When an electrical current is supplied to the coil, arotational force is applied to the magnet, which causes a mirrorattached to the galvanometer scanner to rotate. The electrical currentsupplied to the coil may be controlled to dynamically change theposition of the galvanometer mirror. A resonant scanner (which may bereferred to as a resonant actuator) may include a spring-like mechanismdriven by an actuator to produce a periodic oscillation at asubstantially fixed frequency (e.g., 1 kHz). A MEMS-based scanningdevice may include a mirror with a diameter between approximately 1 and10 mm, where the mirror is rotated using electromagnetic orelectrostatic actuation. A voice coil motor (which may be referred to asa voice coil actuator) may include a magnet and coil. When an electricalcurrent is supplied to the coil, a translational force is applied to themagnet, which causes a mirror attached to the magnet to move or rotate.

In an example implementation, the scanner 162 includes a single mirrorconfigured to scan an output beam 170 along a single direction (e.g.,the scanner 162 may be a one-dimensional scanner that scans along ahorizontal or vertical direction). The mirror may be a flat scanningmirror attached to a scanner actuator or mechanism which scans themirror over a particular angular range. The mirror may be driven by oneactuator (e.g., a galvanometer) or two actuators configured to drive themirror in a push-pull configuration. When two actuators drive the mirrorin one direction in a push-pull configuration, the actuators may belocated at opposite ends or sides of the mirror. The actuators mayoperate in a cooperative manner so that when one actuator pushes on themirror, the other actuator pulls on the mirror, and vice versa. Inanother example implementation, two voice coil actuators arranged in apush-pull configuration drive a mirror along a horizontal or verticaldirection.

In some implementations, the scanner 162 may include one mirrorconfigured to be scanned along two axes, where two actuators arranged ina push-pull configuration provide motion along each axis. For example,two resonant actuators arranged in a horizontal push-pull configurationmay drive the mirror along a horizontal direction, and another pair ofresonant actuators arranged in a vertical push-pull configuration maydrive mirror along a vertical direction. In another exampleimplementation, two actuators scan the output beam 170 along twodirections (e.g., horizontal and vertical), where each actuator providesrotational motion along a particular direction or about a particularaxis.

The scanner 162 also may include one mirror driven by two actuatorsconfigured to scan the mirror along two substantially orthogonaldirections. For example, a resonant actuator or a galvanometer actuatormay drive one mirror along a substantially horizontal direction, and agalvanometer actuator may drive the mirror along a substantiallyvertical direction. As another example, two resonant actuators may drivea mirror along two substantially orthogonal directions.

In some implementations, the scanner 162 includes two mirrors, where onemirror scans the output beam 170 along a substantially horizontaldirection and the other mirror scans the output beam 170 along asubstantially vertical direction. In the example of FIG. 2, the scanner162 includes two mirrors, a mirror 180-1 and a mirror 180-2. The mirror180-1 may scan the output beam 170 along a substantially horizontaldirection, and the mirror 180-2 may scan the output beam 170 along asubstantially vertical direction (or vice versa). Mirror 180-1 or mirror180-2 may be a flat mirror, a curved mirror, or a polygon mirror withtwo or more reflective surfaces.

The scanner 162 in other implementations includes two galvanometerscanners driving respective mirrors. For example, the scanner 162 mayinclude a galvanometer actuator that scans the mirror 180-1 along afirst direction (e.g., vertical), and the scanner 162 may includeanother galvanometer actuator that scans the mirror 180-2 along a seconddirection (e.g., horizontal). In yet another implementation, the scanner162 includes two mirrors, where a galvanometer actuator drives onemirror, and a resonant actuator drives the other mirror. For example, agalvanometer actuator may scan the mirror 180-1 along a first direction,and a resonant actuator may scan the mirror 180-2 along a seconddirection. The first and second scanning directions may be substantiallyorthogonal to one another, e.g., the first direction may besubstantially vertical, and the second direction may be substantiallyhorizontal. In yet another implementation, the scanner 162 includes twomirrors, where one mirror is a polygon mirror that is rotated in onedirection (e.g., clockwise or counter-clockwise) by an electric motor(e.g., a brushless DC motor). For example, mirror 180-1 may be a polygonmirror that scans the output beam 170 along a substantially horizontaldirection, and mirror 180-2 may scan the output beam 170 along asubstantially vertical direction. A polygon mirror may have two or morereflective surfaces, and the polygon mirror may be continuously rotatedin one direction so that the output beam 170 is reflected sequentiallyfrom each of the reflective surfaces. A polygon mirror may have across-sectional shape that corresponds to a polygon, where each side ofthe polygon has a reflective surface. For example, a polygon mirror witha square cross-sectional shape may have four reflective surfaces, and apolygon mirror with a pentagonal cross-sectional shape may have fivereflective surfaces.

To direct the output beam 170 along a particular scan pattern, thescanner 162 may include two or more actuators driving a single mirrorsynchronously. For example, the two or more actuators can drive themirror synchronously along two substantially orthogonal directions tomake the output beam 170 follow a scan pattern with substantiallystraight lines. In some implementations, the scanner 162 may include twomirrors and actuators driving the two mirrors synchronously to generatea scan pattern that includes substantially straight lines. For example,a galvanometer actuator may drive the mirror 180-2 with a substantiallylinear back-and-forth motion (e.g., the galvanometer may be driven witha substantially sinusoidal or triangle-shaped waveform) that causes theoutput beam 170 to trace a substantially horizontal back-and-forthpattern, and another galvanometer actuator may scan the mirror 180-1along a substantially vertical direction. The two galvanometers may besynchronized so that for every 64 horizontal traces, the output beam 170makes a single trace along a vertical direction. Whether one or twomirrors are used, the substantially straight lines can be directedsubstantially horizontally, vertically, or along any other suitabledirection.

The scanner 162 also may apply a dynamically adjusted deflection along avertical direction (e.g., with a galvanometer actuator) as the outputbeam 170 is scanned along a substantially horizontal direction (e.g.,with a galvanometer or resonant actuator) to achieve the straight lines.If a vertical deflection is not applied, the output beam 170 may traceout a curved path as it scans from side to side. In someimplementations, the scanner 162 uses a vertical actuator to apply adynamically adjusted vertical deflection as the output beam 170 isscanned horizontally as well as a discrete vertical offset between eachhorizontal scan (e.g., to step the output beam 170 to a subsequent rowof a scan pattern).

With continued reference to FIG. 2, an overlap mirror 190 in thisexample implementation is configured to overlap the input beam 172 andoutput beam 170, so that the beams 170 and 172 are substantiallycoaxial. In FIG. 2, the overlap mirror 190 includes a hole, slot, oraperture 192 through which the output beam 170 passes, and a reflectingsurface 194 that reflects at least a portion of the input beam 172toward the receiver 164. The overlap mirror 190 may be oriented so thatinput beam 172 and output beam 170 are at least partially overlapped.

In some implementations, the overlap mirror 190 may not include a hole192. For example, the output beam 170 may be directed to pass by a sideof mirror 190 rather than passing through an aperture 192. The outputbeam 170 may pass alongside mirror 190 and may be oriented at a slightangle with respect to the orientation of the input beam 172. As anotherexample, the overlap mirror 190 may include a small reflective sectionconfigured to reflect the output beam 170, and the rest of the overlapmirror 190 may have an AR coating configured to transmit the input beam172.

The input beam 172 may pass through a lens 196 which focuses the beamonto an active region 166 of the receiver 164. The active region 166 mayrefer to an area over which receiver 164 may receive or detect inputlight. The active region may have any suitable size or diameter d, suchas for example, a diameter of approximately 25 μm, 50 μm, 80 μm, 100 μm,200 μm, 500 μm, 1 mm, 2 mm, or 5 mm. The overlap mirror 190 may have areflecting surface 194 that is substantially flat or the reflectingsurface 194 may be curved (e.g., the mirror 190 may be an off-axisparabolic mirror configured to focus the input beam 172 onto an activeregion of the receiver 140).

The aperture 192 may have any suitable size or diameter Φ₁, and theinput beam 172 may have any suitable size or diameter Φ₂, where Φ₂ isgreater than Φ₁. For example, the aperture 192 may have a diameter Φ_(i)of approximately 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, or 10 mm, andthe input beam 172 may have a diameter Φ₂ of approximately 2 mm, 5 mm,10 mm, 15 mm, 20 mm, 30 mm, 40 mm, or 50 mm. In some implementations,the reflective surface 194 of the overlap mirror 190 may reflect 70% ormore of input beam 172 toward the receiver 164. For example, if thereflective surface 194 has a reflectivity R at an operating wavelengthof the light source 160, then the fraction of input beam 172 directedtoward the receiver 164 may be expressed as R×[1−(Φ₁/Φ₂)²]. As a morespecific example, if R is 95%, Φ₁ is 2 mm, and Φ₂ is 10 mm, thenapproximately 91% of the input beam 172 may be directed toward thereceiver 164 by the reflective surface 194.

FIG. 3 illustrates a lidar system 200 that includes a polygon mirror 202driven by a motor 204. The lidar system 200 operates in a two-eyeconfiguration, with a first eye 206A and a second eye 206B. The firsteye 206A includes a collimator 210A, a scan mirror 212A, and a receiver214A, and the second eye 206B includes a collimator 210B, a scan mirror212B, and a receiver 214B. The polygon mirror 202 may be in the form ofa rotatable block with multiple reflective surfaces angularly offsetfrom one another along the polygon periphery of the rotatable block. Inthis example implementation, the polygon mirror 202 has six reflectivesurfaces 220A, 220B, . . . 220F; however, the polygon mirror 202 ingeneral can include any suitable number of surfaces, e.g., three, four,five, eight, etc. The motor 204 imparts rotation to the rotatablepolygon mirror 202. The scan mirrors 212A and 212B are configured torotate, in an oscillatory manner within a certain angular range, aboutthe respective axis orthogonal to the axis of rotation of the polygonmirror 202.

A light source 222 can be a fiber laser that includes a seed laserdiode. The output of the light source 222 can be provided to thecollimators 210A and 210B via fiber-optic cables 224A and 224B,free-space coupling, or in any other suitable manner. While the lidarsystem 200 uses collimators coupled to a shared light source, in otherimplementations of this system each eye can include its owndirect-emitted laser diode. The light source 222 in this case can bemade of multiple direct-emitter laser diodes (e.g., high-power laserdiodes) that directly emit the pulses without requiring opticalamplification. The laser diodes can be housed in the respective sensorheads.

In operation, the collimators 210A and 210B direct output beams 226A and226B to the scan mirrors 212A and 212B, respectively. The scan mirrors212A and 212B then reflect these beams toward non-adjacent reflectivesurfaces of the polygon mirror 202, which then directs the output beams226A and 226B to respective fields of regard. Input beams 228A and 228Bare incident on non-adjacent reflective surfaces of the polygon mirror202 and are reflected toward the scan mirrors 212A and 212B,respectively. The input beams 228A and 228B then propagate toward thereceivers 214A and 214B. In other implementations, input and outputbeams from different eyes can be incident on adjacent surfaces of thepolygon mirror.

Referring back to FIG. 1, the scanner 120 in some implementationsincludes a polygon mirror similar to the polygon mirror 202 and one ortwo mirrors similar to the scan mirrors 212A and 212B, depending on thenumber of eyes of the lidar system. The discussion below refersprimarily to the lidar system 100, but it will be understood that,unless explicitly stated otherwise, the techniques for adjusting scanparameters for a ground portion of the field of regard can beimplemented in the lidar system 200.

FIG. 4 illustrates an example configuration in which several componentsof the lidar system 100 or another suitable system may operate to scan a360-degree view of regard. Generally speaking, the field of view of alight source in this configuration follows a circular trajectory andaccordingly defines a circular scan pattern on a two-dimensional plane.All points on the trajectory remain at the same elevation relative tothe ground level, according to one implementation. In this case,separate beams may follow the circular trajectory with certain verticaloffsets relative to each other. In another implementation, the points ofthe trajectory may define a spiral scan pattern in three-dimensionalspace. A single beam can be sufficient to trace out the spiral scanpattern but, if desired, multiple beams can be used.

In the example of FIG. 3, a rotating scan module 230 revolves around acentral axis in one or both directions as indicated. An electric motormay drive the rotating scan module 230 around the central axis at aconstant speed, for example. The rotating scan module 230 includes ascanner, a receiver, an overlap mirror, etc. The components of therotating module 230 may be similar to the scanner 120, the receiver 140,and the overlap mirror 115 discussed above. In some implementations, therotating scan module 230 also includes a light source and a controller.In other implementations, the light source and/or the controller aredisposed apart from the rotating scan module 230 and/or exchange opticaland electrical signals with the components of the rotating scan module230 via corresponding links.

The rotating scan module 230 may include a housing 232 with a window234. Similar to the window 157 of FIG. 1, the window 234 may be made ofglass, plastic, or any other suitable material. The window 234 allowsoutbound beams as well as return signals to pass through the housing232. The arc length defined by the window 234 can correspond to anysuitable percentage of the circumference of the housing 232. Forexample, the arc length can correspond to 5%, 20%, 30%, 60%, or possiblyeven 100% of the circumference.

Now referring to FIG. 5, a rotating scan module 236 is generally similarto the rotating scan module 230. In this implementation, however, thecomponents of the rotating scan module 236 are disposed on a platform237 which rotates inside a stationary circular housing 238. In thisimplementation, the circular housing 238 is substantially transparent tolight at the lidar-system operating wavelength to pass inbound andoutbound light signals. The circular housing 238 in a sense defines acircular window similar to the window 234, and may be made of similarmaterial.

One type of lidar system 100 is a pulsed lidar system in which the lightsource 110 emits pulses of light, and the distance to a remote target130 is determined from the time-of-flight for a pulse of light to travelto the target 130 and back. Another type of lidar system 100 is afrequency-modulated lidar system, which may be referred to as afrequency-modulated continuous-wave (FMCW) lidar system. A FMCW lidarsystem uses frequency-modulated light to determine the distance to aremote target 130 based on a modulation frequency of the received light(which is scattered from a remote target) relative to the modulationfrequency of the emitted light. For example, for a linearly chirpedlight source (e.g., a frequency modulation that produces a linear changein frequency with time), the larger the frequency difference between theemitted light and the received light, the farther away the target 130 islocated. The frequency difference can be determined by mixing thereceived light with a portion of the emitted light (e.g., by couplingthe two beams onto an APD, or coupling analog electrical signals) andmeasuring the resulting beat frequency. For example, the electricalsignal from an APD can be analyzed using a fast Fourier transform (FFT)technique to determine the difference frequency between the emittedlight and the received light.

If a linear frequency modulation m (e.g., in units of Hz/s) is appliedto a CW laser, then the distance D from the target 130 to the lidarsystem 100 may be expressed as D=c·Δf/(2 m), where c is the speed oflight and Δf is the difference in frequency between the transmittedlight and the received light. For example, for a linear frequencymodulation of 10¹² Hz/s (or, 1 MHz/μs), if a frequency difference of 330kHz is measured, then the distance to the target is approximately 50meters. Additionally, a frequency difference of 1.33 MHz corresponds toa target located approximately 200 meters away.

The light source 110 for a FMCW lidar system can be a fiber laser (e.g.,a seed laser diode followed by one or more optical amplifiers) or adirect-emitter laser diode. The seed laser diode or the direct-emitterlaser diode can be operated in a CW manner (e.g., by driving the laserdiode with a substantially constant DC current), and the frequencymodulation can be provided by an external modulator (e.g., anelectro-optic phase modulator). Alternatively, the frequency modulationcan be produced by applying a DC bias current along with a currentmodulation to the seed laser diode or the direct-emitter laser diode.The current modulation produces a corresponding refractive-indexmodulation in the laser diode, which results in a frequency modulationof the light emitted by the laser diode. The current-modulationcomponent (and corresponding frequency modulation) can have any suitablefrequency or shape (e.g., sinusoidal, triangle-wave, or sawtooth).

Generating Pixels within a Field of Regard of the Lidar Systems

FIG. 6 illustrates an example scan pattern 240 which the lidar system100 of FIG. 1 can produce. The lidar system 100 may be configured toscan output optical beam 125 along one or more scan patterns 240. Insome implementations, the scan pattern 240 corresponds to a scan acrossany suitable field of regard (FOR) having any suitable horizontal FOR(FOR_(H)) and any suitable vertical FOR (FOR_(V)). For example, acertain scan pattern may have a field of regard represented by angulardimensions (e.g., FOR_(H)×FOR_(V)) 40°×30°, 90°×40°, or 60°×15°. Asanother example, a certain scan pattern may have a FOR_(H) greater thanor equal to 10°, 25°, 30°, 40°, 60°, 90°, or 120°. As yet anotherexample, a certain scan pattern may have a FOR_(V) greater than or equalto 2°, 5°, 10°, 15°, 20°, 30°, or 45°. In the example of FIG. 6,reference line 246 represents a center of the field of regard of scanpattern 240. The reference line 246 may have any suitable orientation,such as, a horizontal angle of 0° (e.g., reference line 246 may beoriented straight ahead) and a vertical angle of 0° (e.g., referenceline 246 may have an inclination of 0°), or the reference line 246 mayhave a nonzero horizontal angle or a nonzero inclination (e.g., avertical angle of +10° or −10°). In FIG. 6, if the scan pattern 240 hasa 60°×15° field of regard, then the scan pattern 240 covers a ±30°horizontal range with respect to reference line 246 and a ±7.5° verticalrange with respect to reference line 246. Additionally, the optical beam125 in FIG. 6 has an orientation of approximately −15° horizontal and+3° vertical with respect to reference line 246. The beam 125 may bereferred to as having an azimuth of −15° and an altitude of +3° relativeto the reference line 246. An azimuth (which may be referred to as anazimuth angle) may represent a horizontal angle with respect to thereference line 246, and an altitude (which may be referred to as analtitude angle, elevation, or elevation angle) may represent a verticalangle with respect to the reference line 246.

The scan pattern 240 may include multiple pixels 242, and each pixel 242may be associated with one or more laser pulses and one or morecorresponding distance measurements. A cycle of scan pattern 240 mayinclude a total of P_(x)×P_(y) pixels 242 (e.g., a two-dimensionaldistribution of P_(x) by P_(y) pixels). For example, the scan pattern240 may include a distribution with dimensions of approximately100-2,000 pixels 242 along a horizontal direction and approximately4-400 pixels 242 along a vertical direction. As another example, thescan pattern 240 may include a distribution of 1,000 pixels 242 alongthe horizontal direction by 64 pixels 242 along the vertical direction(e.g., the frame size is 1000×64 pixels) for a total of 64,000 pixelsper cycle of scan pattern 240. The number of pixels 242 along ahorizontal direction may be referred to as a horizontal resolution orpixel density of the scan pattern 240, and the number of pixels 242along a vertical direction may be referred to as a vertical resolutionor pixel density of the scan pattern 240. As an example, the scanpattern 240 may have a horizontal resolution of greater than or equal to100 pixels 242 and a vertical resolution of greater than or equal to 4pixels 242. As another example, the scan pattern 240 may have ahorizontal resolution of 100-2,000 pixels 242 and a vertical resolutionof 4-400 pixels 242.

Each pixel 242 may be associated with a distance (e.g., a distance to aportion of a target 130 from which the corresponding laser pulse wasscattered) or one or more angular values. As an example, the pixel 242may be associated with a distance value and two angular values (e.g., anazimuth and altitude) that represent the angular location of the pixel242 with respect to the lidar system 100. A distance to a portion of thetarget 130 may be determined based at least in part on a time-of-flightmeasurement for a corresponding pulse. An angular value (e.g., anazimuth or altitude) may correspond to an angle (e.g., relative toreference line 246) of the output beam 125 (e.g., when a correspondingpulse is emitted from lidar system 100) or an angle of the input beam135 (e.g., when an input signal is received by lidar system 100). Insome implementations, the lidar system 100 determines an angular valuebased at least in part on a position of a component of the scanner 120.For example, an azimuth or altitude value associated with the pixel 242may be determined from an angular position of one or more correspondingscanning mirrors of the scanner 120.

In some implementations, the lidar system 100 concurrently directsmultiple beams across the field of regard. In the example implementationof FIG. 7, the lidar system generates output beams 250A, 250B, 250C, . .. 250N etc., each of which follows a linear scan pattern 254A, 254B,254C, . . . 254N. The number of parallel lines can be 2, 4, 12, 20, orany other suitable number. The lidar system 100 may angularly separatethe beams 250A, 250B, 250C, . . . 250N, so that, for example, theseparation between beams 250A and 250B at a certain distance may be 30cm, and the separation between the same beams 250A and 250B at a longerdistance may be 50 cm.

Similar to the scan pattern 240, each of the linear scan patterns 254A-Nincludes pixels associated with one or more laser pulses and distancemeasurements. FIG. 7 illustrates example pixels 252A, 252B and 252Calong the scan patterns 254A, 254B and 254C, respectively. The lidarsystem 100 in this example may generate the values for the pixels252A-252N at the same time, thus increasing the rate at which values forpixels are determined.

Depending on the implementation, the lidar system 100 may output thebeams 250A-N at the same wavelength or different wavelengths. The beam250A for example may have the wavelength of 1540 nm, the beam 250B mayhave the wavelength of 1550 nm, the beam 250C may have the wavelength of1560 nm, etc. The number of different wavelengths the lidar system 100uses need not match the number of beams. Thus, the lidar system 100 inthe example implementation of FIG. 7 may use M wavelengths with N beams,where 1≤M≤N.

Next, FIG. 8 illustrates an example light-source field of view (FOV_(L))and receiver field of view (FOV_(R)) for the lidar system 100. The lightsource 110 may emit pulses of light as the FOV_(L) and FOV_(R) arescanned by the scanner 120 across a field of regard (FOR). Thelight-source field of view may refer to an angular cone illuminated bythe light source 110 at a particular instant of time. Similarly, areceiver field of view may refer to an angular cone over which thereceiver 140 may receive or detect light at a particular instant oftime, and any light outside the receiver field of view may not bereceived or detected. For example, as the scanner 120 scans thelight-source field of view across a field of regard, the lidar system100 may send the pulse of light in the direction the FOV_(L) is pointingat the time the light source 110 emits the pulse. The pulse of light mayscatter off the target 130, and the receiver 140 may receive and detecta portion of the scattered light that is directed along or containedwithin the FOV_(R).

An instantaneous FOV may refer to an angular cone being illuminated by apulse directed along the direction the light-source FOV is pointing atthe instant the pulse of light is emitted. Thus, while the light-sourceFOV and the detector FOV are scanned together in a synchronous manner(e.g., the scanner 120 scans both the light-source FOV and the detectorFOV across the field of regard along the same scan direction and at thesame scan speed, maintaining the same relative position to each other),the instantaneous FOV remains “stationary,” and the detector FOVeffectively moves relative to the instantaneous FOV. More particularly,when a pulse of light is emitted, the scanner 120 directs the pulsealong the direction in which the light-source FOV currently is pointing.Each instantaneous FOV (IFOV) corresponds to a pixel. Thus, each time apulse is emitted, the lidar system 100 produces or defines an IFOV (orpixel) that is fixed in place and corresponds to the light-source FOV atthe time when the pulse is emitted. During operation of the scanner 120,the detector FOV moves relative to the light-source IFOV but does notmove relative to the light-source FOV.

In some implementations, the scanner 120 is configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 100. The lidar system 100 may emit anddetect multiple pulses of light as the scanner 120 scans the FOV_(L) andFOV_(R) across the field of regard while tracing out the scan pattern240. The scanner 120 in some implementations scans the light-sourcefield of view and the receiver field of view synchronously with respectto one another. In this case, as the scanner 120 scans FOV_(L) across ascan pattern 240, the FOV_(R) follows substantially the same path at thesame scanning speed. Additionally, the FOV_(L) and FOV_(R) may maintainthe same relative position to one another as the scanner 120 scansFOV_(L) and FOV_(R) across the field of regard. For example, the FOV_(L)may be substantially overlapped with or centered inside the FOV_(R) (asillustrated in FIG. 8), and the scanner 120 may maintain this relativepositioning between FOV_(L) and FOV_(R) throughout a scan. As anotherexample, the FOV_(R) may lag behind the FOV_(L) by a particular, fixedamount throughout a scan (e.g., the FOV_(R) may be offset from theFOV_(L) in a direction opposite the scan direction).

The FOV_(L) may have an angular size or extent Θ_(L) that issubstantially the same as or that corresponds to the divergence of theoutput beam 125, and the FOV_(R) may have an angular size or extentΘ_(R) that corresponds to an angle over which the receiver 140 mayreceive and detect light. The receiver field of view may be any suitablesize relative to the light-source field of view. For example, thereceiver field of view may be smaller than, substantially the same sizeas, or larger than the angular extent of the light-source field of view.In some implementations, the light-source field of view has an angularextent of less than or equal to 50 milliradians, and the receiver fieldof view has an angular extent of less than or equal to 50 milliradians.The FOV_(L) may have any suitable angular extent Θ_(L), such as forexample, approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2mrad, 3 mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly,the FOV_(R) may have any suitable angular extent Θ_(R), such as forexample, approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2mrad, 3 mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Thelight-source field of view and the receiver field of view may haveapproximately equal angular extents. As an example, Θ_(L) and Θ_(R) mayboth be approximately equal to 1 mrad, 2 mrad, or 3 mrad. In someimplementations, the receiver field of view is larger than thelight-source field of view, or the light-source field of view is largerthan the receiver field of view. For example, Θ_(L) may be approximatelyequal to 1.5 mrad, and Θ_(R) may be approximately equal to 3 mrad.

A pixel 242 may represent or correspond to a light-source field of view.As the output beam 125 propagates from the light source 110, thediameter of the output beam 125 (as well as the size of thecorresponding pixel 242) may increase according to the beam divergenceΘ_(L). As an example, if the output beam 125 has a Θ_(L) of 2 mrad, thenat a distance of 100 m from the lidar system 100, the output beam 125may have a size or diameter of approximately 20 cm, and a correspondingpixel 242 may also have a corresponding size or diameter ofapproximately 20 cm. At a distance of 200 m from the lidar system 100,the output beam 125 and the corresponding pixel 242 may each have adiameter of approximately 40 cm.

A Lidar System Operating in a Vehicle

As indicated above, one or more lidar systems 100 may be integrated intoa vehicle. In one example implementation, multiple lidar systems 100 maybe integrated into a car to provide a complete 360-degree horizontal FORaround the car. As another example, 4-10 lidar systems 100, each systemhaving a 45-degree to 90-degree horizontal FOR, may be combined togetherto form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar systems 100 may be oriented so thatadjacent FORs have an amount of spatial or angular overlap to allow datafrom the multiple lidar systems 100 to be combined or stitched togetherto form a single or continuous 360-degree point cloud. As an example,the FOR of each lidar system 100 may have approximately 1-15 degrees ofoverlap with an adjacent FOR. In particular embodiments, a vehicle mayrefer to a mobile machine configured to transport people or cargo. Forexample, a vehicle may include, may take the form of, or may be referredto as a car, automobile, motor vehicle, truck, bus, van, trailer,off-road vehicle, farm vehicle, lawn mower, construction equipment,forklift, robot, golf cart, motorhome, taxi, motorcycle, scooter,bicycle, skateboard, train, snowmobile, watercraft (e.g., a ship orboat), aircraft (e.g., a fixed-wing aircraft, helicopter, or dirigible),or spacecraft. In particular embodiments, a vehicle may include aninternal combustion engine or an electric motor that provides propulsionfor the vehicle.

In some implementations, one or more lidar systems 100 are included in avehicle as part of an advanced driver assistance system (ADAS) to assista driver of the vehicle in the driving process. For example, a lidarsystem 100 may be part of an ADAS that provides information or feedbackto a driver (e.g., to alert the driver to potential problems or hazards)or that automatically takes control of part of a vehicle (e.g., abraking system or a steering system) to avoid collisions or accidents.The lidar system 100 may be part of a vehicle ADAS that providesadaptive cruise control, automated braking, automated parking, collisionavoidance, alerts the driver to hazards or other vehicles, maintains thevehicle in the correct lane, or provides a warning if an object oranother vehicle is in a blind spot.

In some cases, one or more lidar systems 100 are integrated into avehicle as part of an autonomous-vehicle driving system. In an exampleimplementation, the lidar system 100 provides information about thesurrounding environment to a driving system of an autonomous vehicle. Anautonomous-vehicle driving system may include one or more computingsystems that receive information from the lidar system 100 about thesurrounding environment, analyze the received information, and providecontrol signals to the vehicle's driving systems (e.g., steering wheel,accelerator, brake, or turn signal). For example, the lidar system 100integrated into an autonomous vehicle may provide an autonomous-vehicledriving system with a point cloud every 0.1 seconds (e.g., the pointcloud has a 10 Hz update rate, representing 10 frames per second). Theautonomous-vehicle driving system may analyze the received point cloudsto sense or identify targets 130 and their respective locations,distances, or speeds, and the autonomous-vehicle driving system mayupdate control signals based on this information. As an example, if thelidar system 100 detects a vehicle ahead that is slowing down orstopping, the autonomous-vehicle driving system may send instructions torelease the accelerator and apply the brakes.

An autonomous vehicle may be referred to as an autonomous car,driverless car, self-driving car, robotic car, or unmanned vehicle. Anautonomous vehicle may be a vehicle configured to sense its environmentand navigate or drive with little or no human input. For example, anautonomous vehicle may be configured to drive to any suitable locationand control or perform all safety-critical functions (e.g., driving,steering, braking, parking) for the entire trip, with the driver notexpected to control the vehicle at any time. As another example, anautonomous vehicle may allow a driver to safely turn their attentionaway from driving tasks in particular environments (e.g., on freeways),or an autonomous vehicle may provide control of a vehicle in all but afew environments, requiring little or no input or attention from thedriver.

An autonomous vehicle may be configured to drive with a driver presentin the vehicle, or an autonomous vehicle may be configured to operatethe vehicle with no driver present. As an example, an autonomous vehiclemay include a driver's seat with associated controls (e.g., steeringwheel, accelerator pedal, and brake pedal), and the vehicle may beconfigured to drive with no one seated in the driver's seat or withlittle or no input from a person seated in the driver's seat. As anotherexample, an autonomous vehicle may not include any driver's seat orassociated driver's controls, and the vehicle may perform substantiallyall driving functions (e.g., driving, steering, braking, parking, andnavigating) without human input. As another example, an autonomousvehicle may be configured to operate without a driver (e.g., the vehiclemay be configured to transport human passengers or cargo without adriver present in the vehicle). As another example, an autonomousvehicle may be configured to operate without any human passengers (e.g.,the vehicle may be configured for transportation of cargo without havingany human passengers onboard the vehicle).

In some implementations, a light source of a lidar system is locatedremotely from some of the other components of the lidar system such asthe scanner and the receiver. Moreover, a lidar system implemented in avehicle may include fewer light sources than scanners and receivers.

FIG. 9 illustrates an example configuration in which a laser-sensor link320 includes an optical link 330 and an electrical link 350 coupledbetween a laser 300 and a sensor 310. The laser 300 may be configured toemit pulses of light and may be referred to as a laser system, laserhead, or light source. The laser 300 may include, may be part of, may besimilar to, or may be substantially the same as the light source 110illustrated in FIG. 1 and discussed above. Further, the scanner 302, thereceiver 304, the controller 306, and the mirror 308 may be similar tothe scanner 120, the receiver 140, the controller 150, and the mirror115 discussed above. In the example of FIG. 9, the laser 300 is coupledto the remotely located sensor 310 by a laser-sensor link 320 (which maybe referred to as a link). The sensor 310 may be referred to as a sensorhead and may include the mirror 308, the scanner 302, the receiver 304,and the controller 306. In an example implementation, the laser 300includes a pulsed laser diode (e.g., a pulsed DFB laser) followed by anoptical amplifier, and light from the laser 300 is conveyed by anoptical fiber of the laser-sensor link 320 of a suitable length to thescanner 120 in a remotely located sensor 310.

The laser-sensor link 320 may include any suitable number of opticallinks 330 (e.g., 0, 1, 2, 3, 5, or 10) and any suitable number ofelectrical links 350 (e.g., 0, 1, 2, 3, 5, or 10). In the exampleconfiguration depicted in FIG. 9, the laser-sensor link 320 includes oneoptical link 330 from the laser 300 to an output collimator 340 and oneelectrical link 350 that connects the laser 300 to the controller 150.The optical link 330 may include optical fiber (which may be referred toas fiber-optic cable or fiber) that conveys, carries, transports, ortransmits light between the laser 300 and the sensor 310. The opticalfiber may be, for example, single-mode (SM) fiber, multi-mode (MM)fiber, large-mode-area (LMA) fiber, polarization-maintaining (PM) fiber,photonic-crystal or photonic-bandgap fiber, gain fiber (e.g.,rare-earth-doped optical fiber for use in an optical amplifier), or anysuitable combination thereof. The output collimator 340 receives opticalpulses conveyed from the laser 300 by the optical link 330 and producesa free-space optical beam 312 that includes the optical pulses. Theoutput collimator 340 directs the free-space optical beam 312 throughthe mirror 308 and to the scanner 302.

The electrical link 350 may include electrical wire or cable (e.g., acoaxial cable or twisted-pair cable) that conveys or transmitselectrical power and/or one or more electrical signals between the laser300 and the sensor 310. For example, the laser 300 may include a powersupply or a power conditioner that provides electrical power to thelaser 300, and additionally, the power supply or power conditioner mayprovide power to one or more components of the sensor 310 (e.g., thescanner 304, the receiver 304, and/or the controller 306) via the one ormore electrical links 350. The electrical link 350 in someimplementations may convey electrical signals that include data orinformation in analog or digital format. Further, the electrical link350 may provide an interlock signal from the sensor 310 to the laser300. If the controller 306 detects a fault condition indicating aproblem with the sensor 310 or the overall lidar system, the controller306 may change a voltage on the interlock line (e.g., from 5 V to 0 V)indicating that the laser 300 should shut down, stop emitting light, orreduce the power or energy of emitted light. A fault condition may betriggered by a failure of the scanner 302, a failure of the receiver304, or by a person or object coming within a threshold distance of thesensor 310 (e.g., within 0.1 m, 0.5 m, 1 m, 5 m, or any other suitabledistance).

As discussed above, a lidar system can include one or more processors todetermine a distance D to a target. In the implementation illustrated inFIG. 9, the controller 306 may be located in the laser 300 or in thesensor 310, or parts of the controller 150 may be distributed betweenthe laser 300 and the sensor 310. In an example implementation, eachsensor head 310 of a lidar system includes electronics (e.g., anelectronic filter, transimpedance amplifier, threshold detector, ortime-to-digital (TDC) converter) configured to receive or process asignal from the receiver 304 or from an APD or SPAD of the receiver 304.Additionally, the laser 300 may include processing electronicsconfigured to determine a time-of-flight value or a distance to thetarget based on a signal received from the sensor head 310 via theelectrical link 350.

Next, FIG. 10 illustrates an example vehicle 354 with a lidar system 351that includes a laser 352 with multiple sensor heads 360 coupled to thelaser 352 via multiple laser-sensor links 370. The laser 352 and thesensor heads 360 may be similar to the laser 300 and the sensor 310discussed above, in some implementations. For example, each of thelaser-sensor links 370 may include one or more optical links and/or oneor more electrical links. The sensor heads 360 in FIG. 10 are positionedor oriented to provide a greater than 30-degree view of an environmentaround the vehicle. More generally, a lidar system with multiple sensorheads may provide a horizontal field of regard around a vehicle ofapproximately 30°, 45°, 60°, 90°, 120°, 180°, 270°, or 360°. Each of thesensor heads may be attached to or incorporated into a bumper, fender,grill, side panel, spoiler, roof, headlight assembly, taillightassembly, rear-view mirror assembly, hood, trunk, window, or any othersuitable part of the vehicle.

In the example of FIG. 10, four sensor heads 360 are positioned at ornear the four corners of the vehicle (e.g., the sensor heads may beincorporated into a light assembly, side panel, bumper, or fender), andthe laser 352 may be located within the vehicle (e.g., in or near thetrunk). The four sensor heads 360 may each provide a 90° to 120°horizontal field of regard (FOR), and the four sensor heads 360 may beoriented so that together they provide a complete 360-degree view aroundthe vehicle. As another example, the lidar system 351 may include sixsensor heads 360 positioned on or around a vehicle, where each of thesensor heads 360 provides a 60° to 90° horizontal FOR. As anotherexample, the lidar system 351 may include eight sensor heads 360, andeach of the sensor heads 360 may provide a 45° to 60° horizontal FOR. Asyet another example, the lidar system 351 may include six sensor heads360, where each of the sensor heads 360 provides a 70° horizontal FORwith an overlap between adjacent FORs of approximately 10°. As anotherexample, the lidar system 351 may include two sensor heads 360 whichtogether provide a horizontal FOR of greater than or equal to 30°.

Data from each of the sensor heads 360 may be combined or stitchedtogether to generate a point cloud that covers a greater than or equalto 30-degree horizontal view around a vehicle. For example, the laser352 may include a controller or processor that receives data from eachof the sensor heads 360 (e.g., via a corresponding electrical link 370)and processes the received data to construct a point cloud covering a360-degree horizontal view around a vehicle or to determine distances toone or more targets. The point cloud or information from the point cloudmay be provided to a vehicle controller 372 via a correspondingelectrical, optical, or radio link 370. In some implementations, thepoint cloud is generated by combining data from each of the multiplesensor heads 360 at a controller included within the laser 352 andprovided to the vehicle controller 372. In other implementations, eachof the sensor heads 360 includes a controller or process that constructsa point cloud for a portion of the 360-degree horizontal view around thevehicle and provides the respective point cloud to the vehiclecontroller 372. The vehicle controller 372 then combines or stitchestogether the points clouds from the respective sensor heads 360 toconstruct a combined point cloud covering a 360-degree horizontal view.Still further, the vehicle controller 372 in some implementationscommunicates with a remote server to process point cloud data.

In any event, the vehicle 354 may be an autonomous vehicle where thevehicle controller 372 provides control signals to various components390 within the vehicle 354 to maneuver and otherwise control operationof the vehicle 354. The components 390 are depicted in an expanded viewin FIG. 10 for ease of illustration only. The components 390 may includean accelerator 374, brakes 376, a vehicle engine 378, a steeringmechanism 380, lights 382 such as brake lights, head lights, reverselights, emergency lights, etc., a gear selector 384, and/or othersuitable components that effectuate and control movement of the vehicle354. The gear selector 384 may include the park, reverse, neutral, drivegears, etc. Each of the components 390 may include an interface viawhich the component receives commands from the vehicle controller 372such as “increase speed,” “decrease speed,” “turn left 5 degrees,”“activate left turn signal,” etc. and, in some cases, provides feedbackto the vehicle controller 372.

In some implementations, the vehicle controller 372 receives point clouddata from the laser 352 or sensor heads 360 via the link 370 andanalyzes the received point cloud data to sense or identify targets 130and their respective locations, distances, speeds, shapes, sizes, typeof target (e.g., vehicle, human, tree, animal), etc. The vehiclecontroller 372 then provides control signals via the link 370 to thecomponents 390 to control operation of the vehicle based on the analyzedinformation. For example, the vehicle controller 372 may identify anintersection based on the point cloud data and determine that theintersection is the appropriate location at which to make a left turn.Accordingly, the vehicle controller 372 may provide control signals tothe steering mechanism 380, the accelerator 374, and brakes 376 formaking a proper left turn. In another example, the vehicle controller372 may identify a traffic light based on the point cloud data anddetermine that the vehicle 354 needs to come to a stop. As a result, thevehicle controller 372 may provide control signals to release theaccelerator 374 and apply the brakes 376.

In addition to the components 390, the vehicle 354 may be equipped withsensors and remote system interfaces 391, which can be communicativelycoupled to the vehicle controller 372. The components 391 can include anInertial Measurement Unit (IMU) 392, a Geographic Information System(GIS) interface 304 for obtaining mapping data from a remote server viaa communication network, a positioning unit 396 such as a GlobalPositioning Service (GPS) receiver, etc. The vehicle controller 372 insome cases provides data from the components 391 to the lidar system351.

Example Receiver Implementation

FIG. 11 illustrates an example InGaAs avalanche photodiode (APD) 400.Referring back to FIG. 1, the receiver 140 may include one or more APDs400 configured to receive and detect light from input light such as thebeam 135. More generally, the APD 400 can operate in any suitablereceiver of input light. The APD 400 may be configured to detect aportion of pulses of light which are scattered by a target locateddownrange from the lidar system in which the APD 400 operates. Forexample, the APD 400 may receive a portion of a pulse of light scatteredby the target 130 depicted in FIG. 1, and generate an electrical-currentsignal corresponding to the received pulse of light.

The APD 400 may include doped or undoped layers of any suitablesemiconductor material, such as for example, silicon, germanium, InGaAs,InGaAsP, or indium phosphide (InP). Additionally, the APD 400 mayinclude an upper electrode 402 and a lower electrode 406 for couplingthe ADP 400 to an electrical circuit. The APD 400 for example may beelectrically coupled to a voltage source that supplies a reverse-biasvoltage V to the APD 400. Additionally, the APD 400 may be electricallycoupled to a transimpedance amplifier which receives electrical currentgenerated by the APD 400 and produces an output voltage signal thatcorresponds to the received current. The upper electrode 402 or lowerelectrode 406 may include any suitable electrically conductive material,such as for example a metal (e.g., gold, copper, silver, or aluminum), atransparent conductive oxide (e.g., indium tin oxide), a carbon-nanotubematerial, or polysilicon. In some implementations, the upper electrode402 is partially transparent or has an opening to allow input light 410to pass through to the active region of the APD 400. In FIG. 11, theupper electrode 402 may have a ring shape that at least partiallysurrounds the active region of the APD 400, where the active regionrefers to an area over which the APD 400 may receive and detect theinput light 410. The active region may have any suitable size ordiameter d, such as for example, a diameter of approximately 25 μm, 50μm, 80 μm, 100 μm, 200 μm, 500 μm, 1 mm, 2 mm, or 5 mm.

The APD 400 may include any suitable combination of any suitablesemiconductor layers having any suitable doping (e.g., n-doped, p-doped,or intrinsic undoped material). In the example of FIG. 11, the InGaAsAPD 400 includes a p-doped InP layer 420, an InP avalanche layer 422, anabsorption layer 424 with n-doped InGaAs or InGaAsP, and an n-doped InPsubstrate layer 426. Depending on the implementation, the APD 400 mayinclude separate absorption and avalanche layers, or a single layer mayact as both an absorption and avalanche region. The APD 400 may operateelectrically as a PN diode or a PIN diode, and, during operation, theAPD 400 may be reverse-biased with a positive voltage V applied to thelower electrode 406 with respect to the upper electrode 402. The appliedreverse-bias voltage V may have any suitable value, such as for exampleapproximately 5 V, 10 V, 20 V, 30 V, 50 V, 75 V, 100 V, or 200 V.

In FIG. 11, photons of the input light 410 may be absorbed primarily inthe absorption layer 424, resulting in the generation of electron-holepairs (which may be referred to as photo-generated carriers). Forexample, the absorption layer 424 may be configured to absorb photonscorresponding to the operating wavelength of the lidar system 100 (e.g.,any suitable wavelength between approximately 1400 nm and approximately1600 nm). In the avalanche layer 422, an avalanche-multiplicationprocess occurs where carriers (e.g., electrons or holes) generated inthe absorption layer 424 collide with the semiconductor lattice of theabsorption layer 424, and produce additional carriers through impactionization. This avalanche process can repeat numerous times so that onephoto-generated carrier may result in the generation of multiplecarriers. As an example, a single photon absorbed in the absorptionlayer 424 may lead to the generation of approximately 10, 50, 100, 200,500, 1000, 10,000, or any other suitable number of carriers through anavalanche-multiplication process. The carriers generated in an APD 400may produce an electrical current that is coupled to an electricalcircuit which may perform signal amplification, sampling, filtering,signal conditioning, analog-to-digital conversion, time-to-digitalconversion, pulse detection, threshold detection, rising-edge detection,or falling-edge detection.

The number of carriers generated from a single photo-generated carriermay increase as the applied reverse bias V is increased. If the appliedreverse bias V is increased above a particular value referred to as theAPD breakdown voltage, then a single carrier can trigger aself-sustaining avalanche process (e.g., the output of the APD 400 issaturated regardless of the input light level). The APD 400 that isoperated at or above a breakdown voltage may be referred to as asingle-photon avalanche diode (SPAD) and may be referred to as operatingin a Geiger mode or a photon-counting mode. The APD 400 that is operatedbelow a breakdown voltage may be referred to as a linear APD, and theoutput current generated by the APD 400 may be sent to an amplifiercircuit (e.g., a transimpedance amplifier). The receiver 140 (seeFIG. 1) may include an APD configured to operate as a SPAD and aquenching circuit configured to reduce a reverse-bias voltage applied tothe SPAD when an avalanche event occurs in the SPAD. The APD 400configured to operate as a SPAD may be coupled to an electronicquenching circuit that reduces the applied voltage V below the breakdownvoltage when an avalanche-detection event occurs. Reducing the appliedvoltage may halt the avalanche process, and the applied reverse-biasvoltage may then be re-set to await a subsequent avalanche event.Additionally, the APD 400 may be coupled to a circuit that generates anelectrical output pulse or edge when an avalanche event occurs.

In some implementations, the APD 400 or the APD 400 along withtransimpedance amplifier have a noise-equivalent power (NEP) that isless than or equal to 100 photons, 50 photons, 30 photons, 20 photons,or 10 photons. For example, the APD 400 may be operated as a SPAD andmay have a NEP of less than or equal to 20 photons. As another example,the APD 400 may be coupled to a transimpedance amplifier that producesan output voltage signal with a NEP of less than or equal to 50 photons.The NEP of the APD 400 is a metric that quantifies the sensitivity ofthe APD 400 in terms of a minimum signal (or a minimum number ofphotons) that the APD 400 can detect. The NEP may correspond to anoptical power (or to a number of photons) that results in asignal-to-noise ratio of 1, or the NEP may represent a threshold numberof photons above which an optical signal may be detected. For example,if the APD 400 has a NEP of 20 photons, then the input beam 410 with 20photons may be detected with a signal-to-noise ratio of approximately 1(e.g., the APD 400 may receive 20 photons from the input beam 410 andgenerate an electrical signal representing the input beam 410 that has asignal-to-noise ratio of approximately 1). Similarly, the input beam 410with 100 photons may be detected with a signal-to-noise ratio ofapproximately 5. In some implementations, the lidar system 100 with theAPD 400 (or a combination of the APD 400 and transimpedance amplifier)having a NEP of less than or equal to 100 photons, 50 photons, 30photons, 20 photons, or 10 photons offers improved detection sensitivitywith respect to a conventional lidar system that uses a PN or PINphotodiode. For example, an InGaAs PIN photodiode used in a conventionallidar system may have a NEP of approximately 10⁴ to 10⁵ photons, and thenoise level in a lidar system with an InGaAs PIN photodiode may be 10³to 10⁴ times greater than the noise level in a lidar system 100 with theInGaAs APD detector 400.

Referring back to FIG. 1, an optical filter may be located in front ofthe receiver 140 and configured to transmit light at one or moreoperating wavelengths of the light source 110 and attenuate light atsurrounding wavelengths. For example, an optical filter may be afree-space spectral filter located in front of APD 400 of FIG. 11. Thisspectral filter may transmit light at the operating wavelength of thelight source 110 (e.g., between approximately 1530 nm and 1560 nm) andattenuate light outside that wavelength range. As a more specificexample, light with wavelengths of approximately 400-1530 nm or1560-2000 nm may be attenuated by any suitable amount, such as forexample, by at least 5 dB, 10 dB, 20 dB, 30 dB, or 40 dB.

Next, FIG. 12 illustrates an APD 502 coupled to an examplepulse-detection circuit 504. The APD 502 can be similar to the APD 400discussed above with reference to FIG. 11, or can be any other suitabledetector. The pulse-detection circuit 504 can operate in the lidarsystem of FIG. 1 as part of the receiver 140. Further, thepulse-detection circuit 504 can operate in the receiver 164 of FIG. 2,the receiver 304 of FIG. 9, or any other suitable receiver. Thepulse-detection circuit 504 alternatively can be implemented in thecontroller 150, the controller 306, or another suitable controller. Insome implementations, parts of the pulse-detection circuit 504 canoperate in a receiver and other parts of the pulse-detection circuit 504can operate in a controller. For example, components 510 and 512 may bea part of the receiver 140, and components 514 and 516 may be a part ofthe controller 150.

The pulse-detection circuit 504 may include circuitry that receives asignal from a detector (e.g., an electrical current from the APD 502)and performs current-to-voltage conversion, signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. The pulse-detectioncircuit 504 may determine whether an optical pulse has been received bythe APD 502 or may determine a time associated with receipt of anoptical pulse by the APD 502. Additionally, the pulse-detection circuit504 may determine a duration of a received optical pulse. In an exampleimplementation, the pulse-detection circuit 504 includes atransimpedance amplifier (TIA) 510, a gain circuit 512, a comparator514, and a time-to-digital converter (TDC) 516.

The TIA 510 may be configured to receive an electrical-current signalfrom the APD 502 and produce a voltage signal that corresponds to thereceived electrical-current signal. For example, in response to areceived optical pulse, the APD 502 may produce a current pulsecorresponding to the optical pulse. The TIA 510 may receive the currentpulse from the APD 502 and produce a voltage pulse that corresponds tothe received current pulse. The TIA 510 may also act as an electronicfilter. For example, the TIA 510 may be configured as a low-pass filterthat removes or attenuates high-frequency electrical noise byattenuating signals above a particular frequency (e.g., above 1 MHz, 10MHz, 20 MHz, 50 MHz, 100 MHz, 200 MHz, or any other suitable frequency).

The gain circuit 512 may be configured to amplify a voltage signal. Asan example, the gain circuit 512 may include one or morevoltage-amplification stages that amplify a voltage signal received fromthe TIA 510. For example, the gain circuit 512 may receive a voltagepulse from the TIA 510, and the gain circuit 512 may amplify the voltagepulse by any suitable amount, such as for example, by a gain ofapproximately 3 dB, 10 dB, 20 dB, 30 dB, 40 dB, or 50 dB. Additionally,the gain circuit 512 may also act as an electronic filter configured toremove or attenuate electrical noise.

The comparator 514 may be configured to receive a voltage signal fromthe TIA 510 or the gain circuit 512 and produce an electrical-edgesignal (e.g., a rising edge or a falling edge) when the received voltagesignal rises above or falls below a particular threshold voltage V_(T).As an example, when a received voltage rises above V_(T), the comparator514 may produce a rising-edge digital-voltage signal (e.g., a signalthat steps from approximately 0 V to approximately 2.5 V, 3.3 V, 5 V, orany other suitable digital-high level). As another example, when areceived voltage falls below V_(T), the comparator 514 may produce afalling-edge digital-voltage signal (e.g., a signal that steps down fromapproximately 2.5 V, 3.3 V, 5 V, or any other suitable digital-highlevel to approximately 0 V). The voltage signal received by thecomparator 514 may be received from the TIA 510 or the gain circuit 512and may correspond to an electrical-current signal generated by the APD502. For example, the voltage signal received by the comparator 514 mayinclude a voltage pulse that corresponds to an electrical-current pulseproduced by the APD 502 in response to receiving an optical pulse. Thevoltage signal received by the comparator 514 may be an analog signal,and an electrical-edge signal produced by the comparator 514 may be adigital signal.

The time-to-digital converter (TDC) 516 may be configured to receive anelectrical-edge signal from the comparator 514 and determine an intervalof time between emission of a pulse of light by the light source andreceipt of the electrical-edge signal. The output of the TDC 516 may bea numerical value that corresponds to the time interval determined bythe TDC 516. In some implementations, the TDC 516 has an internalcounter or clock with any suitable period, such as for example, 5 ps, 10ps, 15 ps, 20 ps, 30 ps, 50 ps, 100 ps, 0.5 ns, 1 ns, 2 ns, 5 ns, or 10ns. The TDC 516 for example may have an internal counter or clock with a20 ps period, and the TDC 516 may determine that an interval of timebetween emission and receipt of a pulse is equal to 25,000 time periods,which corresponds to a time interval of approximately 0.5 microseconds.Referring back to FIG. 1, the TDC 516 may send the numerical value“25000” to a processor or controller 150 of the lidar system 100, whichmay include a processor configured to determine a distance from thelidar system 100 to the target 130 based at least in part on an intervalof time determined by a TDC 516. The processor may receive a numericalvalue (e.g., “25000”) from the TDC 516 and, based on the received value,the processor may determine the distance from the lidar system 100 to atarget 130.

Example Fiber Laser Implementation

FIG. 13 illustrates an example light source 520 that can operate as thelight source 110 in the lidar system of FIG. 1 or a similar lidarsystem. The light source 520 includes a seed laser 522 and an amplifier524. The light source 520 in various implementations includes one ormore seed lasers 522 or one or more amplifiers 524. The seed laser 520may include (1) a laser diode (e.g., a DFB laser) driven by a pulsegenerator, (2) a wavelength-tunable laser configured to produce light atmultiple wavelengths, (3) multiple laser diodes configured to producelight at multiple respective wavelengths, or (4) any other suitablelaser source. The seed laser 522 may produce low-power optical pulses,and one or more optical amplifiers 524 may be configured to amplify thelow-power pulses to produce amplified pulses of light. The amplifiedpulses of light may be emitted as output beam 125. As an example, theamplifier 524 may receive optical seed pulses having an average power ofgreater than or equal to 1 microwatt, and the amplified output pulsesfrom the amplifier 524 may have an average power of greater than orequal to 1 mW. As another example, the amplifier 524 may receive opticalseed pulses having a pulse energy of greater than or equal to 1 pJ, andthe amplified output pulses from the amplifier 524 may have a pulseenergy of greater than or equal to 0.1 μJ.

The amplifier 524 may be referred to as a fiber amplifier, opticalamplifier, fiber-optic amplifier, optical amp, or amp. In variousimplementations, all or part of an amplifier 524 may be included inlight source 110. The amplifier 524 may include any suitable number ofoptical-amplification stages. As an example, the amplifier 524 mayinclude one, two, three, four, or five optical-amplification stages. Inone implementation, the amplifier 524 includes a single-pass amplifierin which light makes one pass through the amplifier 524. In anotherimplementation, the amplifier 524 includes a double-pass amplifier inwhich light makes two passes through the amplifier gain medium. In somecases, the amplifier 524 may act as a preamplifier (e.g., an amplifierthat amplifies seed pulses from a laser diode or the seed laser 522), amid-stage amplifier (e.g., an amplifier that amplifies light fromanother amplifier), or a booster amplifier (e.g., an amplifier thatsends a free-space output beam 125 to a scanner of the lidar system). Apreamplifier may refer to the first amplifier in a series of two or moreamplifiers, a booster amplifier may refer to the last amplifier in aseries of amplifiers, or a mid-stage amplifier may refer to anyamplifier located between a preamplifier and a booster amplifier.

The amplifier 524 may provide any suitable amount of optical power gain,such as for example, a gain of approximately 5 dB, 10 dB, 20 dB, 30 dB,40 dB, 50 dB, 60 dB, or 70 dB. As an example, the amplifier 524 (whichmay include two or more separate amplification stages) may receivepulses with a 1-μW average power and produce amplified pulses with a 5-Waverage power, corresponding to an optical power gain of approximately67 dB. As another example, the amplifier 524 may include two or moreamplification stages each having a gain of greater than or equal to 20dB, corresponding to an overall gain of greater than or equal to 40 dB.As another example, the amplifier 524 may include three amplificationstages (e.g., a preamplifier, a mid-stage amplifier, and a boosteramplifier) having gains of approximately 30 dB, 20 dB, and 10 dB,respectively, corresponding to an overall gain of approximately 60 dB.

In the light source 520, an optical fiber may convey optical pulsesamplified by amplifier 524 to an output collimator that produces afree-space optical beam 125. The optical fiber may convey, carry,transport, or transmit light from one optical component to another, maybe referred to as a fiber-optic cable, a fiber, an optical link, afiber-optic link, or a fiber link. An optical fiber may includesingle-mode (SM) fiber, large-mode-area (LMA) fiber, multi-mode (MM)fiber, polarization-maintaining (PM) fiber, photonic-crystal orphotonic-bandgap fiber, gain fiber (e.g., rare-earth-doped optical fiberfor use in an optical amplifier), multi-clad fiber (e.g., a double-cladfiber having a core, inner cladding, and outer cladding), or any othersuitable optical fiber, or any suitable combination thereof. As anexample, an optical fiber may include a glass SM fiber with a corediameter of approximately 8 μm and a cladding diameter of approximately125 μm. As another example, an optical fiber may include aphotonic-crystal fiber or a photonic-bandgap fiber in which light isconfined or guided by an arrangement of holes distributed along thelength of a glass fiber. In particular embodiments, one end of anoptical fiber may be coupled to, attached to, or terminated at an outputcollimator. An output collimator may include a lens, a GRIN lens, or afiber-optic collimator that receives light from a fiber-optic cable andproduces the free-space optical beam 125.

The amplifier 524 can be implemented as illustrated in FIG. 14. Theamplifier 524 in this example implementation includes a pump laser 530,a pump 532, and a gain fiber 534. In operation, the pump laser 530pumps, or provides with energy, the gain fiber 534.

The optically pumped gain fiber 534 provides optical gain to particularwavelengths of light traveling through the gain fiber 534. The pumplight and the light to be amplified may both propagate substantiallythrough the core of the gain fiber 534. The gain fiber 534 (which may bereferred to as optical gain fiber) may be an optical fiber doped withrare-earth ions, such as for example erbium (Er³⁺), neodymium (Nd³⁺),ytterbium (Yb³⁺), praseodymium (Pr³⁺), holmium (Ho³⁺), thulium (Tm³⁺),or any other suitable rare-earth element, or any suitable combinationthereof. The rare-earth dopants (which may be referred to as gainmaterial) absorb light from the pump laser 530 and are “pumped” orpromoted into excited states that provide amplification to particularwavelengths of light through stimulated emission. The rare-earth ions inexcited states may also emit photons through spontaneous emission,resulting in the production of amplified spontaneous emission (ASE)light by the amplifier 524. In an example implementation, the amplifier524 with erbium-doped gain fiber 534 may be referred to as anerbium-doped fiber amplifier (EDFA) and may be used to amplify lighthaving wavelengths between approximately 1520 nm and approximately 1600nm. The gain fiber 534 in some implementations is doped with acombination of erbium and ytterbium dopants and may be referred to as aEr:Yb co-doped fiber, Er:Yb:glass fiber, Er:Yb fiber, Er:Yb-doped fiber,erbium/ytterbium-doped fiber, or Er/Yb gain fiber. The amplifier 524with Er:Yb co-doped gain fiber may be referred to as anerbium/ytterbium-doped fiber amplifier (EYDFA). An EYDFA may be used toamplify light having wavelengths between approximately 1520 nm andapproximately 1620 nm. The gain fiber 534 doped with ytterbium may bepart of a ytterbium-doped fiber amplifier (YDFA). A YDFA may be used toamplify light having wavelengths between approximately 1000 nm andapproximately 1130 nm. The gain fiber 534 doped with thulium may be partof a thulium-doped fiber amplifier (TDFA). A TDFA may be used to amplifylight having wavelengths between approximately 1900 nm and approximately2100 nm.

Adjusting Scan Parameters Based on Ground Detection

FIG. 15 illustrates an example scene within a field of regard 600 of alidar system operating in a certain vehicle. The field of regard 600 hasa certain horizontal angular span and a certain vertical angular span.The field of regard 600 overlaps a region of ground ahead of thevehicle. The corresponding portion of the field of regard, which may bereferred to as the “ground portion,” is schematically illustrated asbeing enclosed by a polygon 602. The scene includes a road with roadmarkings 604, a vehicle 606 traveling on the road approximately tenmeters ahead and in the next lane to the right of the vehicle, arelatively distant region 608 covered by the ground portion of the fieldof regard, illuminated by the lidar system at a relatively low grazingangle, other vehicles, other objects such as trees (including thosebeyond the maximum range of the lidar system, etc.). Because of thevehicle 606, the ground portion 602 of the field of regard has a longervertical angular span on the left side and in the middle of the field ofregard 600, as illustrated in FIG. 15.

The term “ground” herein can refer to the road on which the vehicle istravelling, particularly the portion of road directly ahead of thevehicle, but also the road located to the sides and rear of the vehicleas well as any median, sidewalk, shoulder, crosswalk, or bike pathlocated on or near the road. This can include the lane in which thevehicle is located as well as any adjacent lanes and the shoulder of theroad. Further, when the vehicle is travelling through a tunnel, thewalls and even the ceiling may have markings similar to the roadmarkings. The lidar system may treat the walls of a tunnel and, in someimplementations or scenarios, the ceiling of the tunnel as groundportions of the field of regard. Accordingly, in one example scenario,the ground portion has a relatively long vertical angular span on theleft side of the as well as on the right side of the field of regard, toinclude the walls (at least up to a certain elevation, which may bedynamically determined or fixed at 2 m, 2.5 m, 3 m, or any othersuitable value), and a shorter vertical angular span in the middle ofthe field of regard.

FIG. 16 is a flow diagram of an example method 620 for adjusting one ormore scan parameters when the field of regard includes a ground portion,which can be implemented in a lidar system. For example, the method 620can be implemented in the controller 150 (FIG. 1), the controller 306(FIG. 9), the vehicle controller 372 (FIG. 10), etc. In any case, themethod 620 can be implemented as a set of instructions stored on anon-transitory computer-readable medium and executable by one or moreprocessors. For convenience, the discussion below refers primarily tothe lidar system in connection with such steps as detecting the distanceto points on the ground, selecting the pulse power, selecting the scanrate, etc., but it will be understood that in some implementations thesedecisions are implemented in a controller of an autonomous vehicleresponsible for other automated decisions related to maneuvering andotherwise controlling the vehicle (e.g., the vehicle controller 372 ofFIG. 10).

The method 620 begins at block 622, where the ground portion of thefield of regard is identified. To this end, the lidar system can use thedata collected during the previous scan or several prior scans of thefield of regard. In some cases, the lidar system can generate a pointcloud and the controller of the lidar system, and/or a controller of theautonomous vehicle in which the lidar system operates, can identify theground portion of the field of regard using a classifier. In othercases, the lidar system can analyze the shapes of return pulses anddetermine that pixels produced within a portion of the field of regardlikely correspond to locations on the surface of the road or otherwiseon the ground.

As another alternative, the lidar system can determine the cumulativeamount of energy in a set of pulses directed toward a certain region ofinterest by multiplying the amount of energy associated with anindividual pulse (which may be stored in the memory as part ofconfiguration data, for example) by the number of pulses in the set. Thelidar system then can determine the cumulative amount of energy of thereturns corresponding to these pulses, while eliminating the statisticaloutliers in some cases as discussed below, and determine how much of theemitted light the region scatters. The lidar system in this manner canobtain a metric of approximate reflectivity for the region and determinewhether the region is likely a ground region based on this metric. Thelidar system in some cases can eliminate statistical outliers such asranging events that produce no return pulse as well as ranging eventsthat produce high-energy returns, when such ranging events occurindividually or in small sets within larger sets of ranging events thatproduce low-energy returns. For example, a lidar system can consider arelatively large set of pulses defining a contiguous region of interestwithin the field of regard (e.g., 30% of the total number of pixels in asingle scan frame that covers the entire field of regard), determinethat the contiguous region of interest produces a low amount ofscattered light and thus has low average reflectivity, and eliminate asoutliers individual returns or small sets of high-energy returns thatmay correspond to puddles of water on the road, for example. Similarly,the lidar system can eliminate outliers that correspond to absentreturns for the corresponding ranging events, so as to distinguishbetween returns that correspond to low amounts of scattered light on theone hand, and absent returns that may correspond to pulses travelingtoward objects disposed beyond the maximum range of the lidar system onthe other hand.

In addition to determining what part of the field or regard overlapswith the ground, the lidar system can determine distances to points onthe ground along the path of the IFOV, and apply these distances whenadjusting the one or more scan parameters. The lidar system candetermine, for example, that the lowest scan line in the field of regardcorresponds to points on the ground 20 meters away, and adjust the pulserepetition frequency for this portion of the field of regard by assumingthat the maximum range of the lidar system for this portion is 20meters.

Further, the lidar system can use data from other sensors to identifythe ground portion of the field of regard. The controller of the lidarsystem can receive data from an external camera, for example (e.g., acamera included in the sensors 158 in FIG. 1), or a vehicle controller(e.g., the vehicle controller 372 of FIG. 10) can provide indications ofwhere the ground is relative to the controller of the lidar system.

Still further, the vehicle equipped with additional sensors such as thesensors and remote system interfaces 391 of FIG. 10 can use positioningdata along with topographical data received from a remote GIS system orstored locally to determine distances to points on the ground.

Referring for clarity to FIG. 17, the vehicle 354 of FIG. 10 can travelalong a downward slope 650, and the ground portion of the field ofregard can take up a relatively small percentage of the total field ofregard, along the vertical dimension. On the other hand, when thevehicle 354 travels along an upward slope 660, the ground portion of thefield of regard can take up a relatively large percentage of the totalfield of regard along the vertical dimension, as illustrated in FIG. 18.For the vehicle 354 traveling along the downward slope 650, distances tothe closest and farthest points on the ground within the field of regardare d1 and d2, and for the vehicle 354 traveling along the upward slope650, distances to the closest and farthest points on the ground withinthe field of regard are d1′ and d2′. As schematically illustrated inFIGS. 17 and 18, the distances can vary depending on road topography.Moreover, lidar systems in different vehicles can be mounted atdifferent heights relative to the ground level, which can further affectthe distances to the points on the ground.

Depending on the implementation, the lidar system can identify theground portion of the field of regard in terms of a single delimiter,such as the vertical angle at which the “horizon” occurs within thefield of regard, i.e., where the ground ends and an area above groundbegins in the absence of obstacles. If desired, however, a lidar systemcan be configured to recognize more complex boundaries of the groundportion, such as the polygon 602 of FIG. 15. In this case, however, thelidar system may need to recognize the boundary of the ground portionalong both the vertical dimension and the horizontal dimension.Accordingly, the lidar system can vary scan parameters in view of bothvertical and horizontal positions within the scan.

Referring again to FIG. 16, the flow next proceeds to block 624, whereone or several scan parameters are adjusted for scanning the groundportion of the field of regard. As indicated above, the lidar system canadjust such scan parameters as scanning rate (which can measured inradians per second, degrees per second, etc.), line density, pulseenergy, pulse repetition frequency, etc. depending on whether the groundportion 602 of the field of regard 600 or another portion of the fieldof regard 600 is being scanned. These adjustments result in a modifiedscan pattern, a modified pulse energy distribution across the field ofregard, or both. The lidar system thus can vary the scan parametersrelated to the light source, the scanner, or both. In variousimplementations or scenarios, the lidar system can increase the densityof scan lines, increase the horizontal resolution (e.g., by decreasingthe scanning rate and/or increasing the pulse repetition frequency,emitting new pulses in response detecting returns rather than atpredefined fixed time intervals), increase both the density of scanlines and the horizontal resolution. As discussed herein, the lidarsystem can modify the scanning rate and the line density by controllinghow quickly one or several mirrors of the scanner pivot, rotate, orotherwise move.

In some implementations, the light source is a direct-emitter laserdiode that directly produces the emitted optical pulses that are scannedacross the field of regard (e.g., the optical pulses from the laserdiode are not amplified by an optical amplifier). In general, when thelight source includes a direct-emitter laser diode, the lidar system canvary the pulse energy and pulse repetition frequency independently ofeach other, as long as the maximum power handling capability of thelaser diode is not exceeded (e.g., to ensure the laser diode does notexperience a thermal failure or optical damage to the output facets).

Alternatively, the light source may be implemented as the light source520 of FIG. 13 and include a pulsed laser diode followed by one or moreoptical-amplification. The lidar system in this case varies the pulseenergy approximately inversely with the pulse repetition frequency.Thus, as the pulse repetition frequency is increased, the pulse energydecreases. As a more specific example, the lidar system can double thepulse repetition frequency and accordingly decrease the pulse energyapproximately by a factor of two. If higher pulse energies are desired,the lidar system may need to operate the fiber laser at a reduced pulserepetition frequency.

In one implementation, the lidar system addresses this limitation bydynamically varying the pump laser power (i.e., vary the power of thepump laser diode(s) that provide optical pumping to the optical gainfiber in the fiber amplifier). Referring to FIG. 14, for example, thelidar system can vary the power of the pump laser 530. Thus, to obtainhigher pulse energy without reducing the pulse repetition frequency, thelidar system can increase the pump laser power supplied to the gainfiber 534. Similarly, to increase the pulse repetition frequency withoutreducing the pulse energy, the lidar system can increase the pump laserpower supplied to the gain fiber 534, while also increasing the pulserepetition frequency of the seed laser diode 522 of FIG. 13.

Because the lidar system can determine the distance from the lidarsystem to the ground along the IFOV of the emitted light pulse, thelidar system can also adjust the output power to account for the factthat a light pulse that is expected to hit the ground after traveling 20meters does not require the same energy as a light pulse that isexpected to hit an object 200 meters away, to consider one example. Thelidar system thus can reduce the output energy of a light pulse when thelidar system expects the light pulse to hit the ground at a distance ofless than the maximum range of the lidar system, or the maximum distanceat which the lidar system is configured to detect targets.

In some cases, however, the lidar system can increase the laser powerand the output energy of a light pulse when the lidar system determineswith a high degree of confidence that a transmitted light pulse shouldhit the ground, but the default light pulse energy is insufficient toallow the lidar sensor to detect a return. For example, when a lightpulse strikes the road at a sufficiently low grazing angle, the lightpulse is reflected by the road and very little light is scattered andreturned to the lidar sensor, making the road difficult to detect. Arelatively high optical absorption of the ground can be an alternativeor additional reason for the low amount of scattered light to travelback to the lidar system when the ground portion of the field of regardis scanned. For example, the road can be made from a dark material thattends to absorb incident light so that a relatively small fraction(e.g., <30%) of the light pulse is scattered. Increasing the energy of alight pulse increases the likelihood that some of the scattered lightwill be detected by the receiver of the lidar system. The energy of thelight pulse in this scenario in some cases may be higher than the energyrequired to detect objects at the default maximum range of the lidarsystem. In some implementations, the lidar system is configured toestimate an angle at which the outbound pulse will be incident on theground, and increase the pulse energy when the angle is below a certainthreshold value.

To vary the scan parameters related to the scanner, such as the scannerillustrated in FIG. 2 or FIG. 3, the lidar system can modify the speedat which one or several mirrors pivot. For example, to decrease thescanning rate along the horizontal dimension to thereby increase thehorizontal resolution, a lidar system that implements the scanner 162 ofFIG. 2 can decrease the speed at which the mirror 180-1 (responsible forscanning pulses of light along the horizontal dimension) pivots aboutthe corresponding axis. More particularly, depending on theimplementation, a controller can provide a corresponding signal to agalvanometer scanner or a motor, for example. To increase the density ofscan lines, on the other hand, the controller can decrease the speed atwhich the mirror 180-2 (responsible for scanning pulses of light alongthe vertical dimension) pivots about the corresponding axis.

When a lidar system implements a scanner with the polygon mirror 202 ofFIG. 3, the controller of the lidar system can decrease the speed atwhich the polygon mirror 202 rotates in order to increase the horizontalresolution. The controller can decrease the speed at which the scanmirrors 212A and 212B rotate about the respective axis to increase theline density.

In some implementations, a lidar system can scan the field of regardaccording to one density of scan lines (corresponding to pixel densityalong the vertical dimension) in the ground portion of the field ofregard, and according to another density of scan lines in the remainingportion of the field of regard. As illustrated in FIG. 19, for example,a scan 700 can include scan lines 702A, 702B, 702C, etc., separated by acertain angular offset, in the portion of the field of regard that doesnot overlap the ground, and scan lines 704A, 704B, 704C, etc., separatedby a smaller angular offset, in the ground portion of the field ofregard. A lidar system similarly can use two values for the horizontalresolution. FIG. 20 illustrates a scan 710 that includes scan lines712A, 712B, 712C, etc., with a certain horizontal resolution, in theportion of the field of regard that does not overlap the ground, andscan lines 714A, 714B, 714C, etc., with a different horizontalresolution, in the ground portion of the field of regard. Moreparticularly, the density of pixels along the horizontal direction inscan lines 712 in this example scenario is higher than the density ofpixels along the horizontal direction in scan lines 714.

FIG. 21 illustrates how the lidar system can vary scan parameters suchas density of scan lines, horizontal resolution, pulse repetitionfrequency, pulse energy, etc. using more than two respective values forthe ground portion of the field of regard and the remaining region,unlike the scans 700 and 710 of FIGS. 19 and 20. When conducting a scanof a field of regarding including a ground portion delimited by verticalangle 720, a lidar system can vary the horizontal resolution accordingto graph 722, vary the pulse repetition frequency according to graph724, and vary pulse energy according to graph 726. The graphs can 722,724, and 726 can correspond to pre-configured values or dynamic valuesthe lidar system or the vehicle controller sets in view of previousscans, for example. The controller of the lidar system for example canimplement a dynamic algorithm or machine learning to select the suitablescan parameters for the ground portion, or combinations of suitable scanparameters (e.g., horizontal resolution in combination with as averagelaser power over time). As another example, the lidar system candetermine the expected distance from the lidar system to a point on theground along the path of the IFOV of the light source, and select acertain horizontal resolution in view of the expected distance.

Thus, a lidar system in some cases combines some of the adjustments ofscan parameters discussed above. For example, the lidar system may useselections or combinations of the increased pulse repetition frequencywith decreased laser power, increased laser power for low-grazing anglecases with decreased, default, or increased pulse repetition frequency,and default laser power for situations in which the ground or road isnot expected to be in the IFOV of the light source. The lidar system maydynamically modify the laser power and pulse repetition frequencycharacteristics based on ground expectations to ensure that the averagepower of the laser during some time period is within the capability ofthe laser of the lidar sensor.

Additionally, the lidar system may keep the average power of the laserat or below a particular threshold power to ensure that the lidar systemcomplies with eye-safety requirements. For example, when scanning acrossa field of regard, the lidar system may increase pulse energy whenscanning the ground at a grazing angle, and decrease the pulse energywhen scanning portions of the field of regard that include objectslocated relatively close to the lidar system (e.g., <30 meters) orobjects that produce a relatively high amount of scattered light.Although the lidar system may vary the pulse energy while scanningacross the field of regard, the overall average optical power emitted bythe lidar system during the scan may remain below a threshold averageoptical power to ensure that the lidar system operates in an eye-safemanner. As another example, the lidar system may vary the pulserepetition frequency when scanning across a field of regard (e.g., usehigher pulse repetition frequency when scanning regions where higherresolution is desired; and scan other regions with lower pulserepetition frequency) so that, overall, the average optical power for ascan across the field of regard remains below a particular thresholdpower.

In some implementations, the lidar system may adjust the pulserepetition frequency and/or the pulse energy based on the amount ofscattered light produced by objects in the field of regard. For example,the lidar system may increase the pulse energy when scanning a region ofthe field of regard with an object that produces a relatively smallamount of scattered light, and decrease the pulse energy when scanningan object that produces a relatively large amount of scattered light.Referring back to FIG. 15, for example, the region 608 can be expectedto produce little scattered light due to the distance, the grazingangle, and in some cases the type of road surface, whereas the vehicle606 may have retroreflectors or simply a highly reflective surface thatproduces a large amount of scattered light, and the road markings 604may produce a large amount of scattered light because of the paint usedto make the markings. In general, objects that produce small amounts ofscattered light (aka low-scatter objects) may include objects beyond aparticular distance (e.g., >150 meters), dark or absorbing objects(e.g., a black tire or the dark surface of a road), or objects that havea relatively high specular reflection (e.g., a mirror). Objects thatproduce large amounts of scattered light (aka high-scatter objects) mayinclude nearby objects (e.g., objects within <20 meters) or brightobjects that produce diffuse scattered light (e.g., a white shirt or awhite road marking).

Referring again to FIG. 16, after adjusting one or more scan parametersat block 624, the flow of the method 620 proceeds to block 626. Thelidar system scans the ground portion of the field of regard inaccordance with the adjusted scan parameters. As a result, the scan ofthe field of regard can produce a high-resolution scan of a portion ofthe field of regard, and/or a more accurate scan due to the improvedallocation of laser power.

For further clarity, FIG. 22 illustrates example timing of outboundpulses the lidar system 100, when the lidar system 100 transmits thenext outbound pulse upon detecting a return rather than upon expirationof a time period of a certain fixed predetermined duration. The pulsetiming diagram 800 schematically illustrates when the controller 150provides signals to the light source 110 to trigger emission of lightpulses. As shown in the pulse timing diagram 800, the period betweenlight pulses varies based on when the receiver 140 detects a returnpulse corresponding to the previous light pulse.

In the illustrated example, after the lidar system 100 emits pulse N,the receiver 140 detects a return pulse corresponding to pulse N after atime interval T1. The controller 150 generates a signal 810 in responseto the determination that the receiver 140 has received pulse N. Thesignal 810 causes the lidar system 100 to emit pulse N+1. For clarity,FIG. 22 also illustrates a short delay between the time pulse N returnsand pulse N+1 leaves the lidar system 100. This delay corresponds to thetime it takes the signal 810 to propagate through the lidar system 100.

The lidar system 100 in the scenario of FIG. 22 emits pulse N+1 but doesnot receive a return pulse corresponding to pulse N+1 in the time T2 ittakes a light pulse to travel to a target disposed at the maximum rangeand return to the lidar system 100. The lidar system 100 in this casegenerates signal 612 and emits next pulse N+2 upon expiration of a timeperiod of duration T2. As FIG. 22 further illustrates, the receiver 140receives a return pulse corresponding to the emitted pulse N+2 after atime period T3. Because T1<T2 and T3<T2 in this case, the lidar systemachieves a higher pulse rate than a fixed pulse rate in which each pairof adjacent pulses is separated by a time interval of duration T2.

General Considerations

In some cases, a computing device may be used to implement variousmodules, circuits, systems, methods, or algorithm steps disclosedherein. As an example, all or part of a module, circuit, system, method,or algorithm disclosed herein may be implemented or performed by ageneral-purpose single- or multi-chip processor, a digital signalprocessor (DSP), an ASIC, a FPGA, any other suitable programmable-logicdevice, discrete gate or transistor logic, discrete hardware components,or any suitable combination thereof. A general-purpose processor may bea microprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

In particular embodiments, one or more implementations of the subjectmatter described herein may be implemented as one or more computerprograms (e.g., one or more modules of computer-program instructionsencoded or stored on a computer-readable non-transitory storage medium).As an example, the steps of a method or algorithm disclosed herein maybe implemented in a processor-executable software module which mayreside on a computer-readable non-transitory storage medium. Inparticular embodiments, a computer-readable non-transitory storagemedium may include any suitable storage medium that may be used to storeor transfer computer software and that may be accessed by a computersystem. Herein, a computer-readable non-transitory storage medium ormedia may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, field-programmable gate arrays(FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs (e.g., compact discs (CDs),CD-ROM, digital versatile discs (DVDs), blue-ray discs, or laser discs),optical disc drives (ODDs), magneto-optical discs, magneto-opticaldrives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes,flash memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECUREDIGITAL cards or drives, any other suitable computer-readablenon-transitory storage media, or any suitable combination of two or moreof these, where appropriate. A computer-readable non-transitory storagemedium may be volatile, non-volatile, or a combination of volatile andnon-volatile, where appropriate.

In some cases, certain features described herein in the context ofseparate implementations may also be combined and implemented in asingle implementation. Conversely, various features that are describedin the context of a single implementation may also be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various implementations have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, ±12%, or ±15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

1. A lidar system comprising: a light source configured to emit pulsesof light; a scanner configured to scan at least a portion of the emittedpulses of light along a scan pattern contained within a field of regardof the lidar system, wherein the field of regard includes a groundportion that overlaps a region of ground located ahead of the lidarsystem; a receiver configured to detect at least a portion of thescanned pulses of light scattered by one or more remote targets; and aprocessor configured to: identify the ground portion of the field ofregard, and when the emitted pulses scan the ground portion of the fieldof regard during a subsequent scan of the field of regard, adjust apulse energy for the ground portion of the field of regard so that thepulse energy for the ground portion is modified relative to anotherportion of the field of regard.
 2. (canceled)
 3. The lidar system ofclaim 1, wherein: the scan pattern comprises scan lines having aparticular density, and the processor is further configured to increasethe density of scan lines when scanning the ground portion of the fieldof regard to perform a higher-resolution scan of the ground portion ofthe field of regard.
 4. The lidar system of claim 3, wherein the scannerincludes: a first mirror configured to pivot or rotate about a firstaxis to scan the emitted pulses of light along a horizontal dimension,and a second mirror configured to pivot around a second axis orthogonalto the first axis to scan the emitted pulses of light along a verticaldimension, wherein to increase the density of scan lines when scanningthe ground portion of the field of regard, the controller is configuredto modify a speed at which the second mirror pivots about the secondaxis.
 5. The lidar system of claim 1, wherein: the scan pattern has aparticular horizontal resolution, and the processor is furtherconfigured to increase the density of pixels along the horizontaldirection for the ground portion of the field of regard.
 6. The lidarsystem of claim 5, wherein: the scan pattern comprises a particularscanning rate, and to increase the horizontal resolution for the groundportion of the field of regard, the processor is configured to decreasethe scanning rate when scanning the ground portion of the field ofregard.
 7. The lidar system of claim 5, wherein: the light source emitsthe pulses of light at a particular pulse repetition frequency; and toincrease the horizontal resolution for the ground portion of the fieldof regard, the processor is configured to increase the pulse repetitionfrequency when scanning the ground portion of the field of regard. 8-10.(canceled)
 11. The lidar system of claim 1, wherein the processor isfurther configured to: decrease the pulse energy of the emitted pulsesof light when the emitted pulses of light scan the ground portion of thefield of regard; and increase the pulse energy when the emitted pulsesof light scan the other portion of the field of regard, so that anaverage power of the emitted pulses of light for the subsequent scan ofthe field of regard is less than or equal to a particular thresholdaverage power.
 12. (canceled)
 13. The lidar system of claim 1, wherein:the processor is further configured to: determine, based on a previousscan of the field of regard, a low-scatter portion of the field ofregard that produces a relatively low amount of scattered light and ahigh-scatter portion of the field of regard that produces a relativelyhigh amount of scattered light, and perform at least one of: increasethe pulse energy when the emitted pulses of light scan the low-scatterportion of the field of regard, and decrease the pulse energy when theemitted pulses of light scan the high-scatter portion of the field ofregard.
 14. The lidar system of claim 1, wherein the processor isfurther configured to: obtain an estimate an absorption of a surface ofthe ground located ahead of the lidar system, and adjust the pulseenergy further in view of the obtained estimate of the absorption. 15.The lidar system of claim 1, wherein the light source comprises: apulsed laser diode configured to produce optical seed pulses; and one ormore optical amplifiers configured to amplify the optical seed pulses toproduce the emitted pulses of light.
 16. The lidar system of claim 15,wherein: each of the one or more optical amplifiers comprises an opticalgain fiber and one or more pump laser diodes that provides an amount ofoptical pump power to the gain fiber; and the processor is furtherconfigured to increase the pulse energy when the emitted pulses of lightscan the ground portion of the field of regard, including increase theamount of optical pump power provided to the gain fiber.
 17. The lidarsystem of claim 1, wherein: the light source comprises a direct-emitterlaser diode configured to produce the emitted pulses of light; and theprocessor is further configured to vary the pulse energy from thedirect-emitter laser diode independently of a pulse repetition frequencyof the direct-emitter laser diode.
 18. A method in a lidar system forscanning a field of regard of the lidar system, the method comprising:identifying, within the field of regard, a ground portion that overlapsa region of ground located ahead of the lidar system; causing a lightsource to emit pulses of light; scanning at least a portion of theemitted pulses of light along a scan pattern contained within the fieldof regard, including adjusting a pulse energy for the ground portion ofthe field of regard so that the pulse energy for the ground portion ismodified relative to another portion of the field of regard; anddetecting at least a portion of the scanned pulses of light scattered byone or more remote targets.
 19. The method of claim 18, whereinidentifying the ground portion of the field of regard includesdetermining one or more locations on the ground based on data from acamera or based on data from the lidar system of a previous scan of thefield of regard.
 20. The method of claim 18, wherein: the scan patterncomprises scan lines having a particular density, and wherein the methodfurther comprises increasing the density of scan lines when scanning theground portion of the field of regard to perform a high-resolution scanof the ground portion of the field of regard.
 21. The method of claim18, wherein: the scan pattern has a particular horizontal resolution,and wherein the method further comprises increasing the horizontalresolution for the ground portion of the field of regard.
 22. The methodof claim 21, wherein: the scan pattern comprises a particular scanningrate, and increasing the horizontal resolution for the ground portion ofthe field of regard includes decreasing the scanning rate when scanningthe ground portion of the field of regard.
 23. The method of claim 21,wherein: the light source emits the pulses of light at a particularpulse repetition frequency; and increasing the horizontal resolution forthe ground portion of the field of regard includes increasing the pulserepetition frequency when scanning the ground portion of the field ofregard.
 24. (canceled)
 25. The method of claim 21, wherein increasingthe horizontal resolution for the ground portion of the field of regardincludes: determining an expected distance from the lidar system to apoint on the ground along a path of an instantaneous field of view(IFOV) of the light source, and selecting a horizontal resolution inview of the expected distance.
 26. The method of claim 18, whereinadjusting the pulse energy includes decreasing the pulse energy of theemitted pulses of light when the emitted pulses of light scan the groundportion of the field of regard.
 27. The method of claim 26, furthercomprising: increasing the pulse energy when the emitted pulses of lightscan the other portion of the field of regard, so that an average powerof the emitted pulses of light for the subsequent scan of the field ofregard is less than or equal to a particular threshold average power.28. The method of claim 18, wherein adjusting the pulse energy for theground portion includes increasing the pulse energy when the emittedpulses of light are incident on points on the ground located ahead ofthe lidar system at glancing angles below a certain threshold value. 29.The method of claim 18, further comprising: determining, based on aprevious scan of the field of regard, a low-scatter portion of the fieldof regard that produces a relatively low amount of scattered light and ahigh-scatter portion of the field of regard that produces a relativelyhigh amount of scattered light, and wherein adjusting the pulse energyfor the ground portion includes at least one of: increasing the pulseenergy when the emitted pulses of light scan the low-scatter portion ofthe field of regard, and decreasing the pulse energy when the emittedpulses of light scan the high-scatter portion of the field of regard.30. An autonomous vehicle comprising: vehicle maneuvering components toeffectuate at least steering, acceleration, and braking of theautonomous vehicle; and a lidar system including: a light sourceconfigured to emit pulses of light, a scanner configured to scan atleast a portion of the emitted pulses of light along a scan patterncontained within a field of regard of the lidar system, wherein thefield of regard includes a ground portion that overlaps a region ofground located ahead of the lidar system, and a receiver configured todetect at least a portion of the scanned pulses of light scattered byone or more remote targets; and a vehicle controller communicativelycoupled to the vehicle maneuvering components and the lidar system, thevehicle controller configured to control the vehicle maneuveringcomponents using the signals generated by the lidar system; wherein thelidar system is configured to: identify the ground portion of the fieldof regard, and when the emitted pulses scan the ground portion of thefield of regard during a subsequent scan of the field of regard, adjusta pulse energy for the ground portion of the field of regard so that thepulse energy for the ground portion is modified relative to anotherportion of the field of regard.
 31. The autonomous vehicle of claim 30,wherein the one or more remote targets comprise the ground or one ormore vehicles.
 32. The autonomous vehicle of claim 30, wherein: thelidar system is included in a vehicle; and the ground portion comprisesat least a portion of a road on which the vehicle is operating.
 33. Theautonomous vehicle of claim 30, wherein the lidar system is configuredto adjust the pulse energy in accordance with commands received from thevehicle controller.
 34. (canceled)
 35. The autonomous vehicle of claim30, wherein: the scan pattern comprises scan lines having a particulardensity, and the scan pattern has a particular horizontal resolution;and the lidar system is further configured to increase at least one of(i) the density of scan lines or (ii) the horizontal resolution whenscanning the ground portion of the field of regard to perform ahigh-resolution scan of the ground portion of the field of regard. 36.(canceled)
 37. The lidar system of claim 1, wherein the processor isfurther configured to: determine an expected distance from the lidarsystem to the ground portion along a path of an instantaneous field ofview of the light source; and wherein the processor is configured toadjust the pulse energy for the ground portion of the field of regard byadjusting the pulse energy in view of the expected distance.
 38. Themethod of claim 18, further comprising: determining an expected distancefrom the lidar system to the ground portion along a path of aninstantaneous field of view of the light source; and wherein adjustingthe pulse energy for the ground portion of the field of regard includesadjusting the pulse energy in view of the expected distance.